, (r <;So /llC l( - '

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GAHNITE AND ITS FORMATION IN THE CONTEXT OF REGIONAL METAMORPHISM AND MINERALIZATION IN THE

NAMAQUALAND METAMORPHIC COMPLEX.

by

JUDITH ANNE HICKS (formerly Evans)

Thesis s~bmitted in fulfilment of the requirements for the degree of Master of Science in the Faculty of Science, University of Cape Town.

Department of Geology

1988

The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non-commercial research purposes only.

Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author.

ABSTRACT

Gahnite (ZnAl204) is commonly associated with sulphide mineralization in metamorphosed massive sulphide deposits, and also occurs in marbles, pegmatites and quartz veins. Its formation has been attributed to the breakdown of Zn-staurolite or desulphidation of sphalerite during metamorphism. The stability of zinc-rich spinels under a wide range of metamorphic conditions in a variety of lithologies results in its persistence in rocks where many other prograde, high temperature minerals and sulphides have been altered. Thfs has resulted in various investigations into its use in exploration and potential for determining metamorphic parameters. With the interest in finding new ore bodies and in determining the metamorphic history and mineralogy in Namaqualand, some gahnite-bearing localities have been investigated in this study.

Gahnite occurs in association with massive sulphide mineralization in the Bushmanland Sequence rocks (Aggeneys Subgroup) of the Namaqualand Metamorphic Complex at Aggeneys and Gamsberg. Gahnite also occurs in quartzites and metapelitic rocks at Achab, 8 km east of Gamsberg and in sillimanite-corundum rocks 35 km north-east of Aggeneys. On Oranjefontein farm, 70 km south-west of Aggeneys 1 co-existing green and blue gahnite occurs in quartzites and garnet-rich rocks in a similar stratigraphic succession to that which occurs in the Bushmanland rocks in the north.

Gahnite mineral chemistry and textural relations indicates that it formed during diagenesis and subsequent metamorphism of precursor sulphide-bearing, aluminous metasediments at Aggeneys, Achab, Swartkoppies and Oranjefontein in the reaction (Spry and Scott, 1987a); Al2Si20s(OH)4 + ZnS + 0.502.-> ZnAl204 + 2Si02 + 2H20 + 0.5S2

Calculated maximum metamorphic conditions are 650 ±50 °C at 4.5 - 5 kbar in northern Namaqualand and 650 - 750 °C at Oranjefontein in central Namaqualand. Conditions of the prevailing metamorphic f(0) 2 were calculated in the metapelitic assemblages at Aggeneys (-16.0 ±0.7), Achab (-15.8 ±0.7) and Oranjefontein (-16.5 ±0.7). It is possible that there is some re-equilibration of gahnite composition and new gahnite formation during subsequent low grade metamorphism. In the quartzites at Aggeneys and Achab textural evidence supports the continued formation of gahnite along fractures

I

J

by infiltration of oxidising metamorphic fluids. Under these circumstances gahnite forms by reactions such as; 2H3Al03 (in H20) + (Zn,Fe)S -> (Zn,Fe)Al20a + H20 + H2S (Moore and Reid, 1988 in press). At Oranjefontein the formation of almost endmember blue gahnite is attributed to alteration of the high grade assemblage by oxidising metamorphic fluids during retrograde, low temperature metamorph1sm, i.e. (Zn,Mg)Al 20a (green gahnite) + Mg-biotite +garnet+ quartz+ H20 -> ZnAl 20a {green gahnite) + chlorite + rutile + hematite + sericite

Minor zoning in gahnite in a massiv~ gahnite rock at Swartkoppi~s is attributed to gahnite growth during decreasing metamorphic temperatures and in a sphalerite-quartz-gahnite assemblage at Aggeneys, to Fe/Zn exchange between gahnite and sphalerite.

It was found that gahnite occurs in a wide variety of assemblages and exhibits a range in composition. This is attributed to the ability of zn~spinel to incorporate increasing quantities of zinc under decreasing metamorphic temperatures and increasing f(0)2 conditions and the complete solid solution between the endmember components of spinel. Gahnite, associated with sulphide mineralization at Aggeneys has the compositional range Ghn70-e2HC1e-30SP3-6• At'Achab gahnite occurs in quartzites and metapelitic schists and has the compositional range Ghnsa-7eHC7-37Sp3-e• In the silli~anite-corundum rocks at Swartkoppies, a wide range of compositions are exhibited by zincian hercynite and gahnite i.e. Grn1e-seH03s-seSPe-1e• · Green gahnite associated with the high grade metamorphic facies at Oranjefontein has the compositional range· Ghnss-6sHC10-17SP20-3a• Retrograde blue gahnite has in excess of 90 mol% gahnite component, less than 10 mol% hercynite and less than 3 mol% spinel.

It is concluded that gahnite compositon is affected by various parameters including bulk chemistry, the composition of co-existing minerals, metamorphic f(0) 2 and temperature. It will be important to determine the host rock lithology if gahnite composition is to be used to imply the presence of zinc sulphides.

II ..

ABSTRACT

Chapter 1.

TABLE OF CONTENTS

INTRODUCTION

1.1 Geological Setting 1.2 Present Investigation l.3 Previous work on Spinels in Namaqualand

Acknowledgement

Chapter 2. GAHNITE MINERAL CHEMISTRY

2.1 Chemistry of Gahnite 2~2 Occurrence of Gahnite .2.3 Gahnite-forming reactions

Chapter 3. GEOLOGICAL SETTING OF STUDY LOCALITIES

3.1 Regional Geology of the Namaqualand Metamorphic

3.2 General Geology of the Bushmanland Sequence 3.3 General Geology of the Study Localities

3.3.1 Aggeneys 3.3.2 Achab 3.3.3 Swartkoppies 3.3.4 Oranjefontein

Chapter 4. GAHNITE IN THE CONTEXT OF MINERALIZATION AND METAMORPHISM AT THE STUDY LOCALITIES

4.1 Introduction

4.2 AGGENEYS 4.2.1 Petrography 4.2.2 Mineral Chemistry. 4.2.3 Metamorphism and f (0)2 4.2.4 Gahnite Formation

4.3 ACHAB 4.3.l Petrography 4.3.2 Mineral Chemistry 4.3.3 Metamorphism and f(0)2 4.3.4 Gahnite Formation

III

Complex

Page I

1 1

3

5

6

6

8

10 12 14 17 21 24 25

28

29

34 45 51

54 58

66 74

Chapter 5.

4.4 SWARTKOPPIES 4.4.1 Petrography 4.4.2 Mineral Chemistry 4.4.3 Metamorphism 4.4.4 Gahnite Formation

4.5 ORANJEFONTEIN 4.5.1 Petrography 4.5.2 Mineral Chemistry 4.5.3 Zoning in Gahnite 4.5.4 Metamorphism and f(0)2 4.5.5 Gahnite Formation

CONCLUSIONS

Page

77

81 84 87

89 99

118

118

124

5.1 Gahnite mineralogy 128 5.2 Appraisal of zinc in minerals associated with gahnite 134 5.3 Compositional zoning in Gahnite 136 5.4 Gahnite in relation to Pressure, Temperature and f(0)2 141 5.6 Gahnite in exploration 148 5.5 Implication,s for mineralization in the Bushmanland rocks 149

REFERENCE LIST

PHOTOGRAPHIC PLATES

Appendix 1. Analytical methods a~d proc~dures Appendix 2. Explanation of geothermometric and f(0)2 calculations Appendix 3. Lists of molecular proportions of gahnite, hercynite

and spinel. List of molecular proportions of endmember garnet from Oranjefontein.

Appendix 4. Mineral Analyses

IV

150

J

ABBREVIATIONS USED IN THE TEXT

Alm almandine Amphi amphibole BIF banded iron formation Biot biotite Cp chalcopyrite Crd cordierite Gal galaxite Ghn gahnite Gn galena Fsp feldspar Epi epidote Gar garnet He hercynite Hem hematite Mt magnetite Muse muscovite Py pyrope Pyr pyrite Pyrr pyrrhotite Pyxm pyroxmangite Qtz quartz Si 11 sillimanite Sp spinel Spess spessartine Sph sphalerite SS solid solution Tourm tourmaline LLD lower detection limit

v

Chapter 1. INTRODUCTION

1.1 Geological Setting

Gahnite, a zinc aluminium spinel is commonly found in association with zinc mineralization or is related to the breakdown of zincian staurolite in a luminous metasedimentary environments, eg. Broken Hill, New South Wales and the Appalachian .Caledonides. In South Africa gahnite occurs in the ore-bearing Bushmanland Group of the Namaqualand Metamorphic Complex.

Recently gahnite has received much attention, because with ever increasing need to find new ore bodies, gahnite has been used as an indicator mineral for exploration purposes, due to its association with massive sulphide deposits and its resistance to weathering.

Although spinel and quartz are incompatible and hercynite-quartz associations are only compatible at granulite grade metamorphism, several studies indicate that the substitution of zinc into spinel or hercynite stabilises the mineral with quartz to amphibdlite or lower grades. Spry (1984) and Wall and England (1979) suggest that gahnite composition may be sensitive to changes in temperature and metamorphic f(0) 2 and f(S) 2 •

The presence of gahnite in highly metamorphosed rocks, and commonly in association with quartz in Namaqualand provides an opportunity to confirm these theories.

1.2 Present Investigation

Gahnite occurs in rocks in the ore-bearing horizons of the Gamsberg zinc deposit (Rozendaal, 1978) and Aggeneys massive sulphide deposit (Ryan et al. (1982) in northern Namaqualand. Figure 1 is a locality map of northern and central-Namaqualand. Gahnite also occurs associated with schists and quartzites on the farm Achab which borders the Gamsberg zinc deposit. Furthermore, very local massive gahnite and gahnite-sillimanite rocks occur on the Swartkoppies sillimanite deposit on the farm Pella Mission, north of Aggeneys and Gamsberg (Fig.1). Near Springbok, gahnite occurs at Vioolskraalberg on the farm Oranjefontein. At this locality, blue and green varieties of gahnite were found to co-exist in quartzites

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r 0 n Pl ~

M" '< 3 Pl -0

0 .... I ::I

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M" :T (l) "1 ::I

Pl ::I a. n (l)

::I M" "1 Pl ~

z 2 Pl 3 Pl

.Q c Pl ~

Pl ::I a.

0 20 100 km

1~ ~~\\\I NAMAQUALAND METAMORPHIC COMPLEX

17 18 19 20

and schists in rocks which are believed to be correlatives of the Bushmanland Sequence (Hicks et al., 1985, Strydom 1982).

The work reported on here includes the study of gahnite-bearing lithologies found at Swartkoppies, Achab farm, Broken Hill and Black Mountain at Aggeneys and Oranjefontein farm in Namaqualand (Fig.1). Detailed mapping and sample collection was done at the localities of Achab and Oranjefontein. Samples from Swartkoppies, Broken Hill and Black Mountain were made available to the author by J.Moore. The study includes a mineralogic and petrographic appraisal of gahnite and associated assemblages in order to establish the stability relations of the mineral in the context of regional metamorphism •. Microprobe studies of gahnite and associated minerals were done to determine the extent of zinc substitution into mineral phases coexisting with gahnite. Other important aspects of this study include the formation of gahnite in the rocks and a comparison of gahnite composition with those reported in available literature.

According to Spry (1982a, 1984), gahnite associated with massive sulphide mineralization has high zinc and iron contents and low magnesium content. Bernier et al. (1984) found that the ratio of ZnO/ZnO+FeO+MgO in gahnite and·staurolite is related to its position relative to mineralized zones and thus an increase in the ratio could indicate the presence of underlying sulphide ores. Ririe and Foster (1984) found gahnite-bearing sillimanite gneiss a potential directional indicator for mineralization. It is one of the aims of this study to elucidate any lithological or compositional characteristic of gahnite which may be associated with its proximity to mineralization.

• 1.3 Previous Work in Namaqualand

Exsolved zincian spinels from magnetite with up to 14 wt% ZnO are reported from hypersthene-,plagioclase-,phlogopite-,magnetite-,sulphide-bearing noritoids at the O'Okiep mine in Nababeep by Stumpfl et al.(1976). Zincian spinels with 15 wt% ZnO are reported from quartz-,feldspar-,sillimanite-gneiss associated with cupriferous- and magnetite-rich zones from the Kouberg Synform south east of Nababeep (Rozendaal, 1982). Zincian hercynites of similar composition are reported in association with mineralisation in the Kielder District by Gorton (1981).

'; : .• r.'·f>

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. f - ---------------------'----'--"----------------------

Lipson (1978) records the presence of trace quantities of gahnite in the aluminous schist and calc silicate rocks from the Big Syncline ore body at Aggeneys • De Waal (1981), Ryan (1982) and Ryan et al. (1982) observed gahnite in association with the ore horizons at Broken Hill. Spry (1986, 1987a) and Spry and Scott (1986a) studied zincian spinel and gahnite in sulphide-rich rocks, garnet quartzites and quartz-magnetite rocks from Black Mountain and Broken Hill ore bodies at Aggeneys. It was found that gahnite associated with massive sulphides is zinc-rich, (65-85 mol% gahnite component), in comparison to gahnite in the garnet quartzites (18-75 mol%) and magnetite quartzite (20-76 mol%).

At Gamsberg Rozendaal (1982) found that gahnite occurs mostly in the C member above the ore horizon where it has a compositional range of Ghn77-7aHC1s-1aSP3-s• In the B member (ore horizon) gahnite is less common and has the composition Ghn3aHCssSP3•

'

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ACKNOWLEDGEMENT

I am very grateful to Professor A.M. Reid for his encouragement and assistance during this project and to Dr. J.M. Moore who was instrumental in initiating it and who willingly took over supervision when Professor Reid left U.C.T. The C.S.I.R. provided all important funding for a substantial portion of the analytical work and SOEKOR allowed me the use of essential typing, copying and photographic facilities in its compilation. Furthermore I would like to thank the following people whose assistance and expertise in their various fields has been of invaluable help to me ; Dr. D.W. Waters, Dr. P.G. Spry, J.H. Mc Stay, D.S. Rickard. I would also like to acknowledge the support given by the-Precambrian Research Unit at U.C.T. in allowing me to make use of their drafting facilities as well as time generously given by Ms R.M. Kovats. Finally I would like to acknowledge the patience and kindness of the many friends and family both inside U.C.T. and out, whose support was always

there when needed.

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Chapter 2. GAHNITE MINERAL CHEMISTRY

2.1 Chemistry of gahnite

Gahnite, ZnA1 204, is a member of the aluminium Spinel Series of the Spinel Group which also includes a Magnetite Series (Fe 3 +) and Chromite Series (Cr). The structure of the spinel group has 32 oxygens and 24 cations, of which 8 are in 4-fold coordination (A position) and 16 in 6-fold coordination (8 positi6n). Gahnite (ZnAl204) along with spinel (MgAl204), hercynite (FeAl204) and galaxite (MnAl204) are normal spinels with 8 R+ 2 cations in A and 16 R+ 3 in B, as opposed to inverse spinels like magnetite Fe3 +(Fe2+, Fe 3 +)04 or franklinite Fe3 +(Zn2+, Fe 3 +)Q4 with 8 R+ 2 in A and 8 R+2 + 8 R+ 3 cations in B (Deer et al. 1969). ZnAl204, MgAl204 and FeA1 2 04 appear to be miscible in all proportions (Deer et al. 1980, Rumble 1976). The wide variety of compositions exhibited by the Spinel Group minerals enable them to accurately reflect the bulk rock composition of the rocks in which they occur (Rumble, 1976).

2.3 Occurrence of gahnite

Gahnite is named after the Swedish chemist J.G. Gahn and was apparently recorded as early as 1907 (Simpson, 1931). Early references to gahnite include documentation of its occurrence associated with ore-bearing pegmatites (Eskola 1914, Simpson 1930, 1937). Andersen et al. (1937) analysed blue gahnite from the gem gravels of Ceylon and attributed the unusual blue colour to Fe2+ in the mineral structure. Generally gahnite is reported as having a blue-green colour (Deer et al., 1980). Pehrman (1948), discussed Zn-Fe exchange in spinel and proposed a hydrothermal origin for spinel in pegmetites. An early reference by Rankin and Merwin (1918), makes note of the incompatibility of spinel (MgAl 204 ) and quartz which react to form sapphirine, garnet and sillimanite, and cordierite with increasing quantities of quartz (Friedman, 1954). Von Knorring and Dearnley (1960), documented the structural characteristics of gahnite. Several early authors record gahnite as a mineral associated with zinc mineralization (Haranczyk and Skiba 1961, Segnit 1961, Vokes 1962, Salotti 1965, Frondel and Klein 1965, Nemec 1972)~

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Gahnite occurs in a variety of sedimentary, metamorphic and pegmatitic environments. The occurrence of gahnite in sedimentary environments is attributed to its resistance to weathering. Gahnite occurs as an accessory phase in quartz-feldspar pegmatites (Eskola 1914, Simpson 1930, Pehrman 1948, von Knorring and Dearnley 1959, Batchelor and Kinnaird 1984). Weathering of such pegmatites probably produces the detrital gahnite found in sedimentary rocks (Hutton, 1957). Gahnite is infrequently reported from granitic environments (Tulloch, 198i and Stevenson, 1985). In pegmatites and granites the origin of zinc in gahnite is attributed to closely associated ore lodes. However, Tulloch (1981) proposed that gahnite formed in a highly evolved, garnetiferous-, muscovite-, alkali-feldspar granite by late-stage breakdown-of muscovite and concentration of zinc into late-stage aqueous solutions.

In metamorphic rocks gahnite occurs in metapelitic and cordierite­orthoamphibole schists and gneisses. Common assemblages observed are: staurolite + muscovite/biotite +quartz+ sillimanite/andalusite +

I

magnetite + gahnite (± K feldspar, plagioclase, garnet, cordierite) and cordierite + orthoamphibole +quartz+ gahnite (± staurolite, cummingtonite). Its presence is most commonly attributed to retrograde breakdown of zinc-rich staurolite, desulphidation of sphalerite under oxidising metamorphic conditions or prograde metamorphism of zinc-bearing sediments. Although staurolite, biotite, muscovite and chlorite may contain significant quantities of zinc in their structures, in aluminous, zinc-rich terranes, gahnite is a common phase.

Gahnite appears to be stable over a range of metamorphic temperatures and is reported from quartz veins, (Gandhi, 1971), low temperature chlorite-sericite schists (Haranczyk and Skiba, 1961), slates (Kramm, 1977) and in a contact metamorphic aureole (Schumacher, 1985). It is stable in the presence of quartz (Kramm 1978, Dietvorst 1980, Schumacher 1985) and also in highly aluminous rocks (Atkin 1978, Spry 1982b, Feenstra 1985). More specifically it is found in cordierite-anthophyllite rocks associated with minera·11zation (Essene et al. 1982, Wolter and Siefert 1984, Schreurs and Westra 1985, Treloar et al. 1981).

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Gahnite is a common accessory phase and may even constitute a major mineral in metamorphosed massive sulphide deposits e.g. the stratiform massive sulphide deposits of Broken Hill, Australia (Segnit 1961, Hobbs 1975, Plimer 1977), the massive sulphide deposits of the Appalachians (Sandhaus 1981, Craig 1983, Field and Haggerty 1984) and Scandinavian Caledonides (Vokes 1962, Sundblad 1982, Spry 1983, Spry and Scott 1986b} and the Colorado Precambrian massive sulphide.deposits (Sheridan and R~ymond 1977, 1984, Karlsson et al. 1980}. Gahnite is reported as an exsolution product of franklinite at the Franklin and Sterling Hill Zn-Fe-Mn deposits, New Jersey (Frondel and Klein 1965, Frondel and Baum 1974). Gahnite is also reported from Cu-Zn Skarns (Salotti, 1965) and an Archean iron formation in association with zinc mineralization (Appel, 1986).

2.4 Gahnite-forming reactions

Various reactions have been put forward to explain the formation of gahni.te in metamorphic rocks. These include reactions which occur during prograde metamorphism of zinc-bearing sediments and prograde and retrograde metamorphism of precursor zinc-bearing minerals. Some o.f the proposed reactions are listed below.

1. from zinc adsorbed onto sediments which are subsequently metamorphosed e.g. Zn (oxide/sulphide/carbonate) +kaolinite = gahnite +quartz + water (Kramm 1978, Karlsson et al. 1980, Appel 1986, Segnit 1981, Field and Haggerty 1984) • .

2. from breakdown of a zinc-bearing aluminosilicate phase e.g. (i} Zn biotite + sillimanite +quartz= cordierite + gahnite +fluid

(Dietvorst, 1980) or (ii} Zn staurolite + biotite +quartz= sillimanite + K-feldspar + rutile

+Zn hercynite +garnet+ fluid (Stoddard 1976, 1979). Zn staurolite =Zn hercynite + cordierite + sillimanite (Atkin, 1978). Zn staurolite +Sn phlogopite = cordierite +corundum+ gahnite + nigerite + hogbomite + Sn-poor phlogopite (Spry, 1982b). Zn staurolite +muscovite+ quartz+ 02 = andalusite +Zn hercynite +magnetite+ biotite + H2 0 (Schumacher, 1985).

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3. by desulphidation of sphalerite during metamorphism e.g. Gedrite + sphalerite (+staurolite) + 02 = gahnite +quartz+ S2 + H20 (Plimer 1977, Sundblad 1982, Williams 1983, Bernier et al. 1984). Sphalerite + pyrite/pyrrhotite + aluminosilicate + 02 = gahnite + quartz + S2 or Almandine + sphalerite + S2 = gahnite + pyrite + quartz (Spry and Scott 1986 a,b, Spry 1984).

4. in pegmatites and quartz veins from hydrothermal solutions permeating through sulphide-bearing rocks e.g. Zn 2+ + Al 3 + + 4H20 = gahnite +SH+ (Hobbs, 1975). 2KH2Al03 (in fluid)+ sphalerite = gahnite (+ H2S + 2KOH in fluid) (Moore and Reid, 1988 in press).

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Chapter 3. GEOLOGICAL SETTING OF THE STUDY LOCALITIES

3.1 Regional geology of the Namaqualand Metamorphic Complex

The Namaqualand Metamorphic Complex (NMC) covers a large section of northern and central Namaqualand (Fig.l). It consists of a variety of intrusive, metasedimentary and metavolcanic rock units which have undergone extensive deformation ~ccompanied by regional metamorphism (Table 1). The lithologies enco~ntered at the study localities are· correlated with the Bushmanland Sequence which comprises a pretectonic metasedimentary sequence within the NMC (Table 1).

The NMC supracrustal rocks represent a major, east west striking, mobile belt. Deformation varies extensively across the Namaqua province and various interpretations have been applied to the tectonic and stratigraphic units encountered e.g. Joubert (1971) and Blignault et al. (1983). The latter define two main episodes of deformation related to the Namaqua Orogeny. A regional early planar fabric defines the first event. The large-scale intrusion of syntectonic augen gneisses of the Little Namaqua Suite are closely related to an episode of major thrusts and isoclinal folding. To the north of the Aggeneys area, the Groothoek thrust (1000 - 1200 Ma) resulted in the superposition of the calc­alkaline, metavolcanic Orange River Group over the metaquartzite/schist, Aggeneys metasediments. Joubert's (1971) Fl and F2 deformational events are included in this'deformational episode.

The second deformational event occurred in the period 1000 to 1100 Ma and is seen as late, macroscopic upright and open to gentle folds on a regional scale (Joubert 1971, Blignault et al. 1983). Late shears imp,art the last regionally important structural imprint (Joubert 1971, Moore 1977, Blignault et al. 1983) and caused the major deflections in the regional li~eation pattern.

In western Namaqualand metamorphic events relate to the two structural episodes described above. Early planar structures and large-scale intrusive augen gneisses are associated with a high temperature, low pressure, prograde event (Mooie's, 1977 Ml event in the Namiesberg). Waters (1986) describes the metamorphic regime as largely isobaric and suggests that the high temperatures attained are not related to isostatic uplift in the NMC. Upper amphibolite grades metamorphism are recognised in the north (Ryan et al., 1982) and to the south and in the central area a granulite facies zone is recognised (Albat; 1984). In metapelitic schists the transition is; quartz + K-feldspar + plagioclase + biotite +

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Table 1: Lithostratigraphic division of the Namaqualand Metamorphic Complex (after SACS, 1980).

Koperberg Suite

Spektakel Suite

Keimoes Suite Syntectonic intrusive

Hoogoor Suite rock units

Little Namaqualand Suite

Gladkop Suite :• I

Vioolsdrif Suite

Orange River Group

Okiep Group Pretectonic metasedimentary

Bushmanland Group and metavolcanic rock units

Korannaland Group

Marydale and Kaaien Groups

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sillimanite ±garnet_-> quart~+ K~feldspar + plagioclase + cordierite + garnet± biotite ± sillimanite (Moore 1983, Waters and Whales 1984). Several workers (Clifford et al. 1975 a,b, Zelt 1980, Albat 1984, Waters and Whales 1984, Waters and Moore 1985) describe various aspects of the granulite terrain in Namaqualand.

Various retrograde metamorphic signatures relate to the second deformational event of open folding and shearing. The early folds are associated with a lower amphibolite to amphibolite facies metamorphic event (Moore's, 1977 M2 event). Later structures are associated with lower grade, greenschist facies metamorphism (Moore's, 1977 M3 event).

3.2 General geology of the Bushmanland Sequence

The Bushmanland Group comprises a metasedimentary sequence and overlies a basement gneiss complex. SACS (1980) recognises several lithostratigraphic units within the Bushmanland Group including the Pella and Aggeneys Subgroups which were originally described by Joubert (1974) and later in the Namiesberg area by Moore (1977} (Table 2). A more complex stratigraphic succession is recognised by Praekeldt et al. (1983), however their stratigraphic terminology remains informal and is therefore not being used in this thesis.

A generalised succession of the Bushmanland Group in the Pofadder -Aggeneys area is given by SACS (1980). This consists of a basement ' porphyroblastic- and pink gneiss and an overlying metasedimentary sequence which comprises metapelitic schists, metaquartzites, iron formation and an overlying quartz - ~uscovite schist and conglomerate unit. At Aggeneys and Gamsberg, economic barite and massive sulphide mineralization occur within the iron formation. The iron, manganese and barite mineralization is described by Mathias (1941) and Coetzee (1958). Sulphide mineralization at Aggeneys is described by Moore (1974, 1983), Ryan {1982) and Ryan et al. (1982} and at Gamsberg by Rozendaal (1978, 1980, 1982).

At Swartkoppies, on the farm Pella Mission, si·llimanite-corundum rocks constituting an aluminium ore deposit,' occur within the metapelitic schist unit. Several workers have described various aspects of the aluminous rocks (Coetzee 1941, De Jager and von Backstrom 1961, De Jager 1963, Frick and Coetzee 1974, Joubert 1974 and Moore 1980).

According to Tankard et al. (1982) the Bushmanland Sequence above the pink gneiss represents an accumulation of sediments in a shallow basin or

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Table 2: Lithostratigraphy of the Bushmanland Group (after SACS, 1980).

/

Quartz - muscovite schist and conglomerate unit

Iron Formation Unit

Metaquartzite Unit

Schist Unit

Mafic gneisses with intercalated metasediments

Leucocratic gneisses with intercalated metasediments

Quartz - muscovite schist and conglomerate unit

Garns Formation (irdn formation)

Metaquartzite

Namies Schist Formation

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Pella

Guadom

Hom

Aggeneys

basins. The association of concentra~on~ of Al, Ca, Na and B suggest that the parent rocks consisted of clays and evaporites formed in a sabkha or playa-like environment (Moore, 1977). Although there is some dispute as to the origin of the sediments evidence indicates a sedimentary bas.in (basins) initially filled under terrestrial or marginal marine conditions (Tankard et al., 1982).

3.3 General geology of the study areas

Four gahnite-bearing localities hosted in the Bushmanland Sequence were chosen for the basis of this study. The lithostratigraphy of the Bushmanland Sequence is described by SACS (1980). Table 2 shows the subgroup breakdown. Swartkoppies occurs in Bushmanland rocks which are correlated with the Pella Subgroup. Achab locality is part of the Namiesberg area which is correlated with the Aggeneys Subgroup (Moore, 1977). The fourth study locality, Oranjefontein, occurs in central Namaqualand, somewhat distant from the three geographically close areas in northern Namaqualand (Fig.1). Lithological and stratigraphic similarities with the Bushmanland Sequence at Aggeneys have resulted in this locality being correlated with the Bushmanland Sequence (Hicks et al., 1985). Table 3 compares the generalised stratigraphic succession at the 4 localities. Figure 2 is a comparison of the supracrustal rocks at the study localities and shows the similarities in lithology.and to correlate the gahnite-bearing horizons in the context of the generalised succession. There is some controversy concerning the stratigraphic succession of the iron formation in the Broken Hill ore body compared to that at the Aggeneysberge and Gamsberg. At the Aggeneysberge and Gamsberg the sulphide-bearing iron formation rocks overly the metaquartzite unit whereas at Broken Hill the iron formation occurs below this unit (Ryan et al. 1982, Rozendaal 1982, Moore 1986).

The Aggeneys ore bodies, Swartkoppies and Achab are believed to be part of the amphibolite facies zone of the NMC. At Oranjefontein, the presence of biotite-cordierite-garnet rocks associated with quartz­feldspar-cordierite-biotite schist indicates a transitional facies which achieved close to granulite grade metamorphism (Hicks 1983, Hicks et al. 1985). Ryan et al. (1982), Moore (1977) and Rozendaal (1978) recognise three metamorphic events in the Aggeneys area for which Tankard et al. (1982) quotes maximum estimated metamorphic conditions of 690 °C at 3 - 5 kbar.

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basins. The association of concentrat,ons of Al, Ca, Na and B suggest that the parent rocks consisted of clays and evaporites formed in a sabkha or playa-like environment (Moore, 1977). Although there is some dispute as to the origin of the sediments evidence indicates a sedimentary basin (basins) initially filled under terrestrial or margi~al marine conditions (Tankard et al., 1982).

3.3 General geology of the study areas

Four gahnite-bearing localities hosted in the Bushmanland Sequence were chosen for the basis.of this study. The lithostratigraphy of the Bushmanland Sequence is described by SACS (1980). Table 2 shows the subgroup breakdown. Swartkoppies occurs in Bushmanland rocks which are correlated with the Pella Subgroup. Achab locality is part of the Namiesberg area which is correlated with the Aggeneys Subgroup (Moore, 1977). The fourth study locality, Oranjefontein, occurs in central Namaqualand, somewhat distant from the three geographically close areas in northern Namaqualand (Fig.1). Lithological and stratigraphic similarities with the Bushmanland Sequence at Aggeneys have resulted in this locality being correlated with the Bushmanland Sequence (Hicks et al., 1985). Table 3 compares the generalised stratigraphic s~ccession at the 4 localities. Figure 2 is a comparison of the supracrustal rocks at the study' localities and shows the similarities in lithology and to correlate the gahnite-bearing .horizons in the context of the generalised succession. There is some controversy concerning the stratigraphic succession of the iron formation in the Broken Hill ore body compared to that at the Aggeneysberge and Gamsberg. At the Aggeneysberge and Gamsberg the sulphide-bearing iron formation rocks overly the metaquartzite unit whereas at Broken Hill the iron formation occurs below this unit (Ryan et al. 1982, Rozendaal 1982, Moore 1986).

The Aggeneys ore bodies, Swartkoppies and Achab are believed to be part of the amphibolite facies zone of the NMC. At Oranjefontein, the presence of biotite-cordierite-garnet rocks associated with quartz­feldspar-cordierite-biotite sthist indicates a transitional facies which

I

achieved close to granulite grade metamorphism (Hicks 1983, Hicks et al. 1985)·. Ryan et al. (1982), Moore (1977) and Rozendaal (1978) recognise three metamorphic events in the Aggeneys area for which Tankard et a~. (1982) quotes maximum estimated metamorphic conditions of 690 °C at 3.- 5 kbar.

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Table 3: Comparison of the stratigraphy in the study areas.

PELLA NAMIESBERG AGGENEYS ORANJEFONTEIN

(SACS 1"980) (Moore 1977) (Ryan et al.1982) (Hicks et al.1985)

Grey Gneiss with schists and minor amphibolites

" Quartz muscovite schist and nodular gneiss with .

amph i bo 1 ite

Magnetite quart-z i te ( Aggeneys · Iron Format ion J

Metaquartzite Metaquartzite Metaquartzite Metaquartzite

qtz-biot-sill-musc qtz-biot-sill-musc qtz-biot-sill-musc qtz-K feld-cord-schist, schist, schist, biot-si 11-gar sill-cor bodies sill-rich rocks, dark quartzites, schist

·I I

amphibolite, amphibolite, calc silicate sill-rich rocks

Porphyroblastic Quartzo- Quartzo- Quartzo-gneiss feldspathic gneiss feldspathic gneiss feldspathic

gneiss

Achab gneiss Porphyroblastic granite gneiss Biotite gneiss

-15-

Swartkoppies

(SACS 1980; de Jager & von Backstrom 1961: Frick & Coetzee 1974)

..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C ca/c silicate

Namiesberg (Achab)

(Moore, 1977)

. .... . . .... . ......

Aggeneys

(Moore 1983; Ryan et a 1., 1982)

Oranjefontein

(Hicks et al., 1985)

musc-slll schist

meta-quartzite

garnet-rich rocks

'0 0 () (.) 0 (I

: ~ ;~ ~ ~ : : : /eucogneiss

V amphibolite G gahnite-bearlng rocks

Figure 2: Comparison of the stratigraphic succession of the supracrustal rocks in the study areas.

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3.3.1 Aggeneys - Broken Hill ore body

The Aggeneys base metal deposits are situated in northern Namaqualand approximately 80 km west of Pofadder and 110 km north east of Springbok (Fig.1). Three separate ore bodies; Black Mountain, Broken Hill and Big . .

Syncline comprise the Aggeneys deposit (Fig.3). Gamsberg zinc deposit is situated approximately 12 km east of Aggeneys and is similar to Aggeneys deposit with respect to stratigraphic position and ore genesis (Rozendaal, 1982). Samples used in this study were obtained from Broken Hill (Fig.4) and Black Mountain.

Four phases of deformation are recognised in Bushmanland rocks at Aggeneys and Gamsberg. The rocks were subjected to metamorphism with an upper limit bordering on granulite grade, which is correlated with the F2 deformation (Joubert, 1971). Retrograde metamorphism followed and largely overprints evidence of the early metamorphic history. Rozendaal (1978) estimated temperatures of 630 - 670 °C and pressures of 2.8 - 4.5 kbar for the high grade event in the Gamsberg, whereas Ryan et al. (1982) obtained temperatures of 670 - 695 °C at 3.4 - 6 kbar at Aggeneys.

The stratigraphic succession of the Namaqualand Metamorphic Complex at Aggeneys consists of a basal augen gneiss and the overlying Bushmanland Sequence (SACS, 1980). At the Aggeneys deposits, the Bushmanland Sequence comprises a basal pink gneiss overlaid by quartz-biotite-muscovite-sil l imanite schists, quartzite and then quartz-feldspar-muscovite-biotite­sillimanite schists. A generalised stratigraphic column according to Ryan et al. (1982) is given in Table 4. The ore bodies associated with banded iron formations (BIF) have a sulphide mineralogy consisting of pyrite, pyrrhotite, sphalerite, galena and chalcopyrite (Ryan et al., 1982).

Various metapelitic rocks and some gahnite-bearing quartzites were obtained from Black Mountain and Dabiepoort, but most of the gahnite-bearing rocks were obtained from Broken Hill (Fig.4).

The ore bodies at Broken Hill consist of a lower sulphide-bearing quartzite, followed· by a succession of banded and massive sulphide and baritic rocks which grade into magnetite amphibolite, BIF and garnet quartzites.

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----------------------------~-------------------------~~~~~~~~--:-~~-:--~----

I 1--'. co I

N

MOUNTAIN

Figure 3:

BIG

BROKEN HILL

0 5000 metres

Geological map of Aggeneys massive sulphide deposit, (modified from Ryan et al., 1982).

Pegmatite

Paragneiss

DAB IE POORT

Meta conglomerate

Amphibolite

Magnetite-rich gossan

Sillimanite quartz schist

Undifferentiated schist

White quartzite

Aluminous schist Fm.

A'!gen and pink gneiss Fm.

I I-' l..O I

Figure 4:

0 50

D Scree

• R:«l lli.81

~ ~ E-3

CJ . .

Magnetite-rich gossan

Ferruginous garnet quartzite

Sillimanite quartz schist

UndifferenHated schist

White quartzite Fm

S A/uminous schist Fm

250 metres

Ore Fm

Geological (modified

map of Broken Hill from Ryan et al

ore deposit, ., 1982).

Aggeneys,

I

Table 4: Stratigraphy of the NMC in western Namaqualand (after Ryan et al., 1980).

Amphibolite I Leucocratic Grey Gneiss Formation

Aggeneys Iron Formation Bushman land

White Quartzite Formation Sequence

Aluminous Schist Formation

Pink Gneiss Formation

Augen Gneiss Formation

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NMC

:• f : . • ' . • • ~ :

Ryan et al.· (1982) have divided the rock types into sulphide, oxide and silicate facies (Table 5). From Black Mountain in the west to Gamsberg in the east, the minerafization shows a progressive decrease in Cu and Pb and increase in Zn (Ryan et al. 1982, Rozendaal 1982)(Table 6). Metal concentrations in the ores are further divided into a Fe-Pb-Cu dominated succession at Black Mountain and Broken Hill in the south-west and a Mn-Zn dominated succession in the Aggeneysberge and at Gamsberg in the

. north-east (Moore, 1983). Genetic model interpretation; based on these and other characteristics of the deposits, emphasise a sedimentary basin environment of deposition with an exhalative source, with Gamsberg representing a deeper, more distal environment (Ryan et al. 1982, Moore 1977).

Gahnite has been observed throughout the mineralized zones (Joubert 1971, Moore 1974, 1980, 1986) and also occurs at the contact of crosscutting pegmatites (Ryan et al., 1982). The formation of gahnite has been attributed to desulphidation of sphalerite (Ryan et al. 1982, Spry 1987a).

3.3.2 Achab

Achab farm is situated approximtely 8 km east of Gamsberg. The areas studied occur along the northern flank bordering Garns Noord farm. The position of the gahnite-rich rocks in relation to the surrounding lithologies is shown in Figure 5.

The lithologies which crop out at this locality comprise a basal leucogneiss (correlated with the pink gnei~s at Broken Hill), with local . bands of calc-silicate rocks and amphibolites towards the base of the unit (Fig.5). This is succeeded by the Namies schist and metaquartzite (Moore, 1977). lmpersistent bands of gahnite-quartz rock, cordierite-anthophyll ite rock, sillimanite-rich rock, tourmalinite and amphibolite occur towards the base of the aluminous schist. The gahnite-quartzites and gahnite-bearing schists occur at the contact between the leucogneiss and the aluminous schist and locally in the upper horizons of the aluminous schist near the contact with the overlying metaquartzite unit.

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'

Table 5: Distribution of mineralization with respect to rock type at Aggeneys massive sulphide deposit (after Ryan et al., 1982).

FACIES ROCK TYPE . MINERALS MINERALIZATION

Silicate Magnetite Amphibolite quartz, magnetite, moderate grunerite, cumming- galena (gn)> tonite, spessartine sphalerite (sp}> fayalite chalcopyrite (cp

Oxide Magnetite quartzite magnetite, quartz, moderate garnet, biotite gn >sp >cp

Ferruginous garnet quartz, magnetite very weak quartzite garnet, biotite sp >cp >gn

Sulphide Massive sulphide pyrrhotite, pyrite high quartz gn > pyrite >cp

Sulphide quartzite I h . moderate-high quartz, pyrr ot1te pyrite gn >sp >cp

Table 6: Zoning of mineralization between Aggeneys and Gamsberg ore deposits (Ryan et al., 1982).

OREBODY BASE METAL CONTENT

WEST Black Mountain 0.75 %Cu 2.67 %Pb 0.59 %Zn

JT Broken Hill 0.34 3.57 1.77

Big Syncline 0.04 1.01 2.45

Gamsberg o.oo 0.50 7.00

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. D quartzite

- metapelitic ~chist

D calc-silicate rock

0 0 0

oo•ooo leucognei~s

~)

ACHAB

Figure 5:

vv

T

G

M

s \~ 0

amphibolite

tourmalinite

gahnite-quartz rock

cordierite-anthophyllite rock

si llimanite· rich rock

..

. . . . . . • NAMIESBERG'

2km

• • .,,A- ... ,-.,, ... . "' ',

....... - :.. .; .... / '\J • • I _.,

~-· .... ,.-..... r, · J /' .. \.. ... "'~, """'• . . . . . ....,

•• , • .. 1 . ""-,,. . :--..,_ . --- ...... . '

Geological map of Achab study locality, (adapted from Moore, 1977).

.,

-23-

The Namiesberg at Achab (Fig.5) has undergone similar polyphase · deformational events to the rocks at Aggeneys (Moore, 1977). Three metamorphic episodes were interpreted to have affected rocks in the Namiesberg (Moore, 1977). These are; Ml, for which temperature estimates of 650 and 750 °C at 5 - 7 kbar are given, M2 at 600 - 500 °C and 3 - 5 kbar and M3 at less than 500 °C and below 3 kbar pressur~ (Moore, 1977).

3.3.3 Swartkoppies

Swartkoppies sillimanite-corundum deposit is situated on Pella Mission farm approximately 30 km north-west of Pofadder and 35 km north-east of Aggeneys in northern Namaqualand (Fig.1). It was first described by Coetzee (1~41) and the discovery of further sillimanite deposits in northern Namaqualand led to follow up investigations by de Jager and von Backstrom (1961), Frick and Coetzee (1974) and Moore (1977). SACS (1980) correlates the rocks at this locality with the Pella Subgroup of the Bushmanland Sequence (Table 2). Table 3 lists the stratigraphic succession in the area.

The sillimanite-corundum rocks occur as massive bodies jn a basal biotite-sillimanite schist. The schist has been correlated with the Aluminous Schist of the Bushmanland Sequence at Aggeneys (Praekelt et al., 1983). The .sillimanite-corundum rock consists of radiating fibrolite masses which merge into colourless sillimanite prisms containing corundum cores and ilmenite inclusions (Coetzee, 1941). Biotite-sillimanite schist overlies the sillimanite-corundum rock. Massive quartzite forms the uppermost unit in the Pella area. Limonite specks in the basal schist horizon infer the former presence of sulphides (SACS, 1980). Massive gahnite and gahnite-fibrolite roc~s crop out locally in the sillimanite­corundum rock. Secondary copper staining was observed at the sampling locality (Moore, pers. comm.)._ Similar sillimanite-corundum rocks occur in Achab Pan and are interpreted to result from progressive metamorphism of high aluminium clays (Moore, 1977,1980)

-24~

3.3.4 Oranjefontein

Oranjefontein farm is situated in western, central Namaqualand approximately 50 km east of Springbok and 70 km south-west of Aggeneys (Fig.1). Gahnite-bearing lithologies occur on a prominent hill, Vioolskraalberg, in the northwest section of Oranjefontein farm. A geological map of the area is shown in Figure 6.

Vioolskraalberg forms part of a narrow belt of paragneisses enclosed within pretectonic and syntectonic gneisses which form a basal intrusive suite of porphyroblastic grey gneisses in the Little Namaqualand Suite (SACS, 1980). Vioolskraalberg is a flat lying, synformal structure which is correlated with the F3 deformational episode of the Namaqualand Metamorphic Complex (Joubert, 1971). The stratigraphic succession at Vioolskraalberg bears strong resemblance to the lower portions of the Bushmanland Group, as described by SACS (1980), which host the base metal sulphide deposits of Aggeneys and Gamsberg (Table 3).

The basal unit in the vicinity of Vioolskraalberg is a coarse-grained, biotite gneiss, which is locally overlain by lenses of pink weathering, leucocratic, quartzo-feldspathic gneiss. This is succeeded by weathered, brown, aluminous schist. A thick succession of massive, coarsely crystalline, white quartzite forms the uppermost unit at this locality.

Dark green, crystalline spinel coexists with bright blue spinel in a variety of rock types at the interface between the aluminous schist and overlying quartzites (Fig.6). The gahnite-bearing rocks were first described by Joubert (1971) who linked the presence of blue spinel to late stage quartz pegmatites associated with retrograde shearing at the locality.

Within the aluminous schist are narrow, lense-shaped bodies, not longer than 5 m and approximately 0.5 m thick, consisting of garnet-bearing metapelitic rocks. In the uppermost portions,of the aluminous schist, massive garnet and garnet-biotite schists locally contain gahnite. At the same stratigraphic level are gahnite-quartz rocks containing green and blue gahnite and locally, galena. The gahnite quartzites show greater

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N

........... /++

/+ + /+ +

': : ~ + + t + +

\:: \ + + '+ + +

'\+++

't..: + \+++ \+++

+ + + +

\:.!.!!..t-- \\ \\ l. \

_,,-. '":"" .. ~~-:""" - -l. .,,4++++++++++\\

/+ + + + + + + + + + + + 'l\ I+ + + + + + + + + + + + +\\ \+++++++++++++(\ ~ + + .. ,..<"" + + + + + + + •1 \ ,. ;r · 12 + + + + + + + + '\."I.

' 1 . y .. + + + + + + + + +, ... + + + + + + + + + + + ·'" \+ + + + + + + + + + +..,.: .....\. \. '-'•++++++;, ....... "--·.....: ...... "'-"..,,.

100m

• uJ • • I.If"/ • •

+ + --..... ~· + + +

....... . · ...... . . , ... ,

..

...... .. , .. ··~ ;....._

......... . ·, . ;, :-..... .

...... . . ·,_ . ...... . ~ • .1

• 1 . i . t .. . . ~ . . , -:~

. . .

·I • 1 . i

I

l . ~ ·1

. . i ..

. . I . I

... ,.,,..:. + + + + + + + + +

·-·-·-·-·-~~·.••++ ++++++ ... Bi?f'j"' ~!:..:_r.·~ -·.-..~-*-+...t .+...t.t...+ + ,.. .... -----~

...... ._ .. _; ! . .+....: !_+..!. t...•...:t..1-...:.,,... ·- ·-·- ~-·-·-·-:I

Quartzite

Ouartz-gahnite rocks

Garnet-rich rocks

Metapelitic schist

Leucogneiss

Biotite gneiss

Shear

-.- Foliation

.- lineation ./

_,,,. Farm boundary ,/

Figure 6: Geological map of Oranjefontein, (~dapted from Hicks et al., 1985).

-26-

(.

' ,-

r I

I

' ,.

'i

: ~ '

lateral persistence than the massive garnet and garnet-biotite rocks which are restricted to lenses preserved within a major synformal fold closure (Fig.5). In the lower horizons of the massive quartzite, fine-grained blue gahnite fills cracks and fissures and appears to radiate outward from green gahnite cores. Locally, galena and specks of chalcopyrite occur in the lower horizons of the massive quartzite unit. On the southern flanks of Vioolskraalberg at the contact between the schist and quartzite, a green epidote-chlorite contains up to five percent galena.

To the south of Oranjefontein, metapelitic rocks are dominated by granulite facies quartz-K feldspar-garnet-cordierite gneisses (Joubert 1971, Moore 1983,1986, Albat 1984, Waters and Whales 1984, Waters and Moore 1985).and to the north in the Aggeneys/Gamsberg area by quartz-biotite- muscovite-sillimanite schists of upper amphibolite grade (Moore 1977, Rozendaal 1978,1982). Pressure-temperature conditions of 700 - 900 °C and 5 - 6 kbar have been estimated for the granulite terrain (Albat 1984) and 650.- 700 °C and 4 - 5 kbar for the amphibolite grade rocks at Aggeneys/Gamsberg (Moore 1983). The garnet-bearing metapelitic rocks contain biotite, cordierite and rarely sillimanite and K feldspar at Oranjefontein, and appear to represent a transitional zone between the granulite and amphibolite facies. Temperatures of 600 - 750 °c at 4.5 - 5 kbar were calculated by Hicks et al. (1985).

-27-

- I

Chapter 4. GAHNITE IN THE CONTEXT OF MINERALIZATION AND METAMORPHISM AT THE STUDY LOCALITIES

4.1 Introduction

The following sections describe gahnite-bearing lithologies at Aggeneys, Achab, Swartkoppies ~nd Oranjefontein. Using petrographic data and mineral analyses an attempt is made to tie the formation of gahnite in to the regional metamorphic history of the Bushmanland rocks in Namaqualand. Geothermometric and oxygen fugacity calculations are applied to metapelitic assemblages. An explanation of the methods employed is given in Appendix 2. Gahnite compositions are compared to similar gahnite occurrences in the literature.

Mineral anaiyses were made on th~ Cam~ca ~i~roprobe in the Geochemistry Department at the University of Cape Town and are listed in Appendix 4. Tables of average analyses of minerals are given in the text: Stoichiometric recalculation of Fe 3 + content of gahnite was necessary for the calculation of endmember compositions. The method used for recalculation is outlined in Appendix 1 and a list of endmember compositions of analysed spin~l is given in Appendix 3.

-28-

________ J

4.2 Aggeneys

4.2.1 Petrography

Samples obtained from the Aggeneys locality include gahnite-bearing quartzite from the Black Mountain ore body and Dabiepoort (east of Aggeneys) and samples of the magnetite quartzite, magnetite amphibolite and massive sulphide horizons at Broken Hill. Estimated modal proportions of most of the samples studied are given in Table 7.

Gahnite-bearing quartzites

Amphibole-,garnet-bearing quartzite from Aggeneys contains pale, pleochroic blue-brown blade-like anthophyllite and gedrite, and small, euhedral garnet grains as major minerals other than quartz. Magnetite, chalcopyrite and green gahnite occur in minor to accessory amounts. The -bright green spinel occurs as'tiny, rounded grains in the matrix or in association with magnetite.

Quartzites obtained from Dabiepoort contain pale-brown biotite, pale green gahnite and accessory quantities of iron oxides, goethite, galena and pyrite.

Various gahnite-bearing samples associated with sulphide-bearing ores were obtained from the Broken Hill ore body. These are described below.

Magnetite quartzite

(1) Banded Magnetite Quartzite. (Figure 7a) Compositionally this rock is almost bimineralic consisting of quartz (> 70%) and magnetite (- 20%). Quartz grains are large (up to 6 mm), strained and tend to be elongate with sutured grain boundaries. Magnetite occurs as elongate grains with ragged outlines; occasionally euhedral forms are present. Magnetite contains 0.2 - 0.4 mm quartz and green hercynite inclusions (Fig.7a). Exsolved hercynite grains most commonly occur along

-29-

Tmm ~

a. Exsolved hercynite in the magnetite­quartzite.

Tmm ~

c. Euhedral gahnite associated with sphalerite, muscovite and quartz in the massive sulphide rocks.

Abbreviations:

0-3mm L.____.J

b~ Porphyroblastic gahnite with rims of muscovite in the massive sulphide rocks. Alteration to sphalerite occurs along cleavage traces.

d. Gahnite rimmed by a stacked corona of sericite, quartz and sphalerite in an embayed garnet grain in the brecciated_ massive sulphide rock.

G - gahnite, Ga - garnet, M - magnetite, Mu - muscovite, Q - quartz, S - sillimanite, Sp - sphalerite, R - rutile.

Figure 7: Textural relations of minerals in rocks from Broken Hill.

-30-

Table 7. Esti!Tl3.ted m:x:lal proportions of minerals present in s~les studied fran Aggeneys

~LE: BH-1 BH-3 BH-i BHL0-1 81-fn'E-1 131-f.o.JE-2 Bffi-3:>2 240AG56 DP

fvlagnetite 3J 15 40 00 20 m Hematite tr Cha lcopyr.ite 5 35 m 10 5 tr Pyrite 15 tr tr Pyrrootite 25 25 10 10 5 m Sphalerite m m 10 5 m m Galena tr 5 40 10 tr tr Quartz 25 5 10 55 45 20 75 75 95 Feldspar 5 m Pyroxmangite 5 5 Garnet 5 m 10 Chlorite m tr tr m tr Biotite 5 tr tr m M.iscovite 5 10 tr Gahnite/hercynite m tr tr tr tr m m Tour!Tl3.line m Anphioole I tr tr 10 Si 11 i!Tl3.ni te tr

'm' indicates minerals present in minor proportions (5% or less) 'tr' indicates minerals present in trace quantities (1% or less)

Rock Types:

BH-1, BH-3 sulphide-, ~ioole-bearing BIF BH-2 : ITl3.ss i ve su 1 phi de rock BHL0-1 : brecciated massive sulphide BM-1, BHn'E-2: sulphide-bearing magnetite quartzite (BIF) 81£3)2 : banded magnetite quartzite (BIF) 240AG56 : anphioole-garnet quartzite DPB-1 : rretaquartzite

-31-

'' .

the edge of magnetite grains, bordering on matrix quartz. The exsolved hercynite contains'tiny magnetite and quartz inclusions. Spinel also occurs as tiny grains in·quartz inclusions in magnetite. Accessory mineral phases in this rock include muscovite and chlorite (Table 7).

(2) Sulphide-rich Magnetite Quartzite. Sulphide minerals include chalcopyrite, pyrrhotite and sphalerite (Table 7). The ore minerals form coarse interlocking grains. Minor phases include garnet, phlogopite, chlorite, muscovite and gahnite. Quartz and magnetite are the major phases with quartz occuring as coarse grains, (0.6 - 4 mm), with undulose extinction and sutured grain boundaries. Euhedral magnetite grains occur throughout the rock. Chalcopyrite and pyrrhotite appear to be associated. Sphalerite, like magnetite occurs throughout the matrix. Pale-green gahnite grains up to 0.35 mm are associated with sulphide minerals and magnetite. Green gahnite is commonly anhedral or occurs· as ribbon-like inclusions in chalcopyrite, pyrrhotite or sphalerite. Sphalerite is commonly spatially associated with gahnite and occasionally surrounds it and infills fractures in gahnite. The association of sphalerite with fractures in gahnite suggests that gahnite is replaced by retrograde sphalerite. Gahnite commonly contains quartz inclusions and shows no disequilibrium features towards quartz. Garnet occurs locally as aggregates interspersed with magnetite and quartz. Garnet and ~ahnite were not observed in contact.

Sulphide-rich amphibole-bearing BIF.

The samples studied include a quartz-, magnetite-dominated assemblage and a sulphide-dominated assemblage, however both rocks contain the mineral suite; quartz + magnetite + chalcopyrite + pyrrhotite + sphalerite + galena+ pyroxmangite + amphibole (Ta~le_7). Quartz is invariably surrounded by a thin rim consisting of small radiating pyroxmangite grains. Pyroxmangite also occurs as pale, (0.4 - 0.8 mm), subhedral grains in the ore assemblage. Amphibole occurs in a blade-like habit, displays excellent twinning, typical amphibole cleavage and has a 2V of 80-90°. Grain size is similar to that of pyroxene. The amphibole contains significant quantities of manganese and appears to fit the description of tirodite described by Ryan et al. (1982). Although sphalerite occurs throughout, no .gahnite was observed in the samples studied •

. -32-

Massive Sulphide. (Figures 7b,c)

This rock contains a sulphide-dominated assemblage. The gangue minerals include quartz as a major phase along with brown phlogopite, colourless muscovite, minor feldspar and pale green gahnite. Sulphides include galena, pyrite, pyrrhotite and sphalerite (Table 7). Quartz occurs as large poikiloblastic grains (up to 1.7 mm). Large phlogopite and muscovite laths coexist with quartz. Most of the orange-brown phlogopite is corroded and altered. In contrast to this, muscovite is unaltered and exhibits euhedral grain shapes. Pale green gahnite occurs throughout the assemblage as inclusions in the ore minerals or along with quartz and muscovite as part of the gangue mineral assemblage (Fig.7c). Where it occurs as inclusions in ore, gahnite forms large anhedral grains commonly bordered by sphalerite and magnetite (Fig.7b). Inclusions of magnetite, sphalerite and rutile occur in gahnite. A feature of gahnite in this assemblage is the narrow rim of muscovite which surrounds the grains and forms a boundary between it and the surrounding sulphides. Small grains of quartz are commonly associated with gahnite in the ore and these too are surrounded by muscovite (Fig.7c). Occasional grains of gahnite are surrounded partially by a narrow rim of quartz. Gahnite surrounded by quartz is generally associated with sphalerite. Large complex gahnite-muscovite-quartz intergrowths on closer inspection comprise inclusions of gahnite and quartz hosted in large, optically continuous muscovite poikiloblasts. Scattered, euhedral grains of gahnite also occur as inclusions in quartz grains in the matrix.

A coarse, brecciated form of the massive sulphide rock consists dominantly of quartz cemented by pyrrhotite, galena and pyrite. Minor sphalerite is present as well as garnet, tourmaline and muscovite (Table 7). The dominant quartz fraction is recrystallised and exhibits a fine mortar texture. Muscovite occurs in elongat~, curved laths with stumpy grain terminations and is generally surrounded by sulphides. Tourmaline occurs as 0.06 - 0.4 mm, rounded grains displaying a yellow-orange/orange pleochroic scheme. Garnet tends to be concentrated locally as subhedral, fractured grains of up to 1.7 mm in diameter. Larger grains contain inclusions of quartz, magnetite and fine sillimanite needles. Garnet is

-33-

commonly fractured and infilled with sulphides. Pale green gahnite is rare, occurring as anhedral grains in muscovite. A single grain of gahnite occurs in an embayment in garnet surrounded by sphalerite. The gahnite grain is surrounded by a stacked corona consisting of an inner· sericite layer, quartz and a wider sphalerite rim (Fig.7d). Quartz and sericite grains surround the complex mineral aggregate.

4.2.2 Mineral Chemistry

Mineral analyses were obtained by use of the Cameca Microprobe in the Geochemistry Department at the University of Cape Town. An explanation of the technique employed and method of data reduction is given in Appendix 1. Natural and synthetic standards were employed. Individual mineral analyses are listed in Appendix 4. Table 8 lists average mineral analyses of the rocks studied.

Muscovite. Muscovite is a major phase in the massive sulphide rocks (Table 8). The simplified general formula for analysed muscovite is: K2Mgo.3-o.3sFeo.4-o.47Tio.13Al3.37(SisAl2l02o(OH)4. There is some substitution of Ti, Mg and Fe for octahedral Al and this site is slightly overfull according to the structural formula. A stoichiometric recalculation of the analysed composition did not require that any of the Fe be present in the Fe3+ state. Individual muscovite grains contained up to 0.23 wt% CaO but most of the analyses contained no calcium. A single analysis of a Na-muscovite was made but the rest have < 0.5 wt% NaO. None of the muscovite analysed contained zinc above the detection limit for this element (0.2 wt% ZnO).

Biotite/Phlogopite In the massive sulphide rock orange-brown biotite occurs along with muscovite, the latter replacing earlier brown biotite. The simplified structural formula for biotite in this sample is: Nao.03K1.7Mno.13Mg3_3Fe1.9Tio.2(Al2.sSis.4)02o(OH)4. Biotite contained significant quantities of manganese (up to 1 wt% MnO). Phlogopite occurs as a minor phase in sulphide-bearing BIF (Table 8), and

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·~-----------'

Table 8. Average (or representative) analyses of minerals present in sarrµles studied at Aggeneys.

BIOTITE PHLOOJPITE

n 7 2 2 1 ~LE Bl-6156-7 Bl-6156-5 BH-2 81-WE-2

<1 CT O'

Si02 34.14 0.91 33.89 0.35 36.91 0.14 41.12 Ti02 4.11 0.34 3.41 0.63 1.84 0~10 0.00 Al203 19.22 0.53 19.49 0.69 17.48 0.42 12.98 Cr203 nd 0.00 0.01 nd nd FeO 24.65 2.17 25.89 1.48 14.57 0.02 9.91 MnO 0.23 0.05 0.24 0.01 0.99 0.01 0.51 M30 5.17 0.55 5.00 0.42 14.26 0.32 21.32 CaO nd nd nd nd ZnO 0.16 0.04 nd Na20 0.07 0.04 0.11 0.01 0.10 0.03 1.02 K20 9.00 0.40 7.61 0.00 8.74 0.00 7.33

Total 96.67 96.32 95.05 94.27

I M.JSCOV ITE CHLORITE

n 1 7 3 1 3 ~LE 81£156-5 81-1-2 BHL0-1 Bl-6156-5 81-WE-2

(j er Si02 45.3) 42.76 0.29 43.64 0.63 29.50 3).42 Ti02 0.59 1.51 0.12 1.35 0.12 2.46 nd Al203 35.50 32.10 0.32 32.02 0.24 21.40 9.56 Cr203 nd nd nd nd nd FeO 1.83 3.12 0.47 2.55 0.13 28.32 43.00 MnO nd 0.07 0.02 o~oo 0.05 0.43 2.04

M30 0.34 1.63 0.07 1.38 Q,Q) 7.63 2.15 .eao nd nd nd nd nd ZnO 0.13 0.12 nd 0.15 Na20 0.22 0.21 0.03 0.51 0.14 0.00 0.14 K20 7.13 9.25 0.11 9.64 2.72 0.32

Total 90.91 90.78 91.18 92.54 88.58

<f 1.25

1.01

0.41 0.03 0.32

o.oo 0.07 0.07

nd: eleirent was not detected or the arrount detected is belOtJ the detection limit of the analytical metroo ef'l1'Jloyed. 6: is a statistical measure of the range of 1n1 nurrt>er of analyses. All Fe was analysed as FeO.

-35-

' I l

' -------- J

Table 8. Average (or representative) analyses of minerals present in sarrples studied at Aggeneys.

PYRO)(fvW.GITE TIRODITE MITHOPHYLLITE GEOOITE TCXR4t\LINE

n 2 5· 1 2 5 SIM'LE BH-1 BH-3 24CWl56 24QA.G56 BHL(}-1

er CJ 6 6

Si02 47.03 0.19 53.14 0.16 9).98 44.55 0.75 35.00 O.fi6 Ti02 nd nd 0.04 0.13 0.02 0.69 0.18 Al203 nd 0.19 0.00 4.14 13.00 0.04 34.01 0.9) Cr203 nd nd nd nd nd FeO 9.3) 1.41 13.97 0.40 24.41 25.fi6 0.32 9.14 1.12 ~ 40.96 2.98 15.71 0.69 0.3) 0.27 0.01 0.22 0.04 MJ) 2.16 1.37 14.40 0.49 18.03 13.58 0.37 4.87 0.75 CaO 0.22 0.10 0.20 o.oo 0.07 0.12 0.00 0.72 0.23 Na20 nd 0.11 0.03 0.26 1.04 0.07 1.00 0.21 K20 nd nd nd nd 0.11 o.a:>

Total 99.67 97.72 98.23 98.41 86.36

Gl\RNET

n 5 5 2 4 3 SPM>LE BHn'E 1 BHLO 1 2400.G56 lffi 156-7 /l1Krl95

cf 6 6 6 6

Si02 36.72 0.20 36.31 0.12 37.37 0.11 37.01 0.16 37.19 0.18 Ti02 nd nd nd nd nd Al203 20.89 0.18 21.52 0.04 21.81 0.28 21.19 0.09 21.16 0.11 FeO 21.67 0.48 24.79 0.00 35.34 0.86 32.74 0.38 34.86 0.13 ~ 17.82 0.75 16.33 0.73 1.24 0.01 8.71 o.a:> 5.73 0.07

~ 1.47 0.09 0.98 0.10 5.3)"' 0.17 1.45 o.oo 1.36 0.07 CaO 1.43 0.36 0.53 0.14 0.34 0.01 1.17 0.04 1.93 0.07 Na20 nd nd nd nd nd K20 nd nd nd nd nd

Total 100.00 100.46 101.40 102.27 102.23

nd: element was not detected or the arrount detected is belOttl the detection limit of the analytical mettxx:I erJl>loyed. 6: is a statistical measure of the range of 'n' nurrber of analyses. All Fe was analysed as FeO.

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Table 8. Average (or representative) analyses of minerals present in saJ'll)les studied at Aggeneys.

~ETITE

n 3 1 4 4 1 SJM>LE BH-1 BH-3 l*E-1 131-WE-2 24CWi.%

0 0 0

Si02 0.02 0.01. nd 0.04 0.02 0.04 0.01 0.(6 Ti02 0.04 0.02 0.21 0.10 0.02 0.15 0.02 0.14 Al203 0.13 o.cs 0.20 0.33 0.04 0.40 O.C6 0.23 Cr203 nd nd nd nd 0.18 FeO 95.23 0.25 92.(6 96.26 0.43 95.82 0.98 95.13 f'lnO 1.76 0.04 2.26 0.33 0.(6 0.35 0.07 nd ~ 0.03 0.03 nd 0.02 0.01 nd nd CaO nd nd nd nd nd ZnO nd nd nd nd 0.14

Total 97.21 94.75 97.(6 96.76 95.00

~ITE

n 11 1 9 10 6 SLM'LE IBH-2 BHL0-1 l*E-1 l*E-2 24CWi.%

0 0 0

Si02 nd nd nd . nd nd Ti02 nd nd nd nd nd Al203 57.04 0.35 58.03 56.69 0.24 56.97 0.41 55.77 Cr203 0.07 0.04 nd nd nd nd FeO 7.12 0.f:() 10.41 9.22 0.31 9.51 1.C6 16.94 f'lnO 0.51 o.cs 0.49 0.38 o.cs 0.56 0.14 nd ~ 1.15 0.11 0.79 1.07 0.(6 1.CS o.cs 2.77 ZnO 33.00 0.57 32.17 32.47 0.44 31.74 1.02 24.10

Total 99.49 101.89 99.83 99.83 99.58

0

< 0.62

1.44

0.16 1.64

nd: element was not detected or the arroont detected is belai1 the detection limit of the analytical metrod errployed. o: is a statistical measure of the range of 'n' m.rrber of analyses. All Fe was analysed as FeO.

SPHl\LERITE

n 3 SLM'LE Blf-2

0

Zn 58.94 O.C6 Fe 8.13 0.07 l'-\'l 0.3) O.C6 s 33.00 0.24

Total 101.17 Zn/Fe 7.2

-37-,

3 CFB-1

0

nd nd

56.79 0.42 0.07 0.03

11.43 0.15 0.41 0.03 0.57 0.02

3).14 0.40

99.41

'J

~:(i .. i. t

-. t •

has the structural formula: Naa.3K1.3Mno.osMg4.sFe1.3Ala.3(Al2Sisl020 (OH)4. It was found to contain less manganese than biotite (0.5 wt% MnO). Stoichiometric recalculation of biotite and phlogopite did not require that any Fe occurs in the Fe3+ state. Analysis for zinc in biotite and phlogopite gave values of less than 0.2 wt% ZnO (0.2 wt% ZnO is the lower detection limit for this element in the analyses).

Chlorite The only chlorite observed in the rocks studied occurred in the phlogopite-bearing BIF (see above). Chlorite is significantly rich in iron and silica and contains in excess of 2 wt% MnO. A simplified formula is Naa.1Ko.1Mgo.7Mno.4Fea.sA11.s(Al1Si7)02o(OH)4.

Garnet In the massive sulphide and sulphide-bearing BIF, garnet has high spessartine contents. Average core compositions of garnet in the samples studied are Almss.7SpeSS37_aPy4Gross1.s and Alm4a.sSpess4a.9PYs.9Gross4.2 respectively. Similar spessartine-almandine garnets are recorded in the aluminous schist at Aggeneys (Ryan et al., 1982) and at Gamsberg (Rozendaal, 1982). Garnet in the Aggeneys garnet-,anthophyllite quartzite has an average composition of Alm7sPY20Spess3Gross1. Garnet compositions are ~lotted on a triangular endmember diagram, Figure 8.

f\; Tourmaline ;~·.) Small quantites of pleochroic orange/yellow tourmaline occur· in the

1y .. brecciated massive sulphide rock. These have a formula of: Naa.sCaa.03Mg1.sFe1.sMno.3Caa.2AlsB3Si1s027 which is equivalent to 44 mol% dravite and 56 mol% schorl endmembers. The total wt% oxides in tourmaline is 85 from which the boron content is estimated at approximately 15 wt% 8203.

Amphibole The sulphide-rich, amphibole-bearing BIF from Broken Hill contains a

. Mn-rich amphibole which is described as tirodite by Ryan et al. (1982). The structural formula of the amphibole is Naa.13Caa.03Mn2.1Fe1.aMg3_3Sia022• Garnet-orthoamphibole

-38-

Figure 8:

SPESSARTINE

•

'

GROSSULAR

Symbols: open triangules: sulphide-rich magnetite quartzite closed circles brecciated massive sulphide open circles metapelitic schist

Garnet compositions (Broken Hill) plotted on a triangular end-member diagram

-39-

quartzite from Aggeneys has coexisting anthophyllite and gedrite e.g. Anthophyllite; Nao.oaCao.01Mno.04Fe3.12Mg4.1Alo.s(Si7.aAlo.02l022 and Gedrite; Nao.31Cao.02Mno.04Fe3.3Mg3.1Al1.3(Sia.sAli.1)022•

Pyroxenite In the magnetite-amphibolite Mn-rich pyroxenite is fairly common. Average analyses yield a structural formula of Cao.01Feo.1aMno.7aMgo.osSi03.

Magnetite Magnetite in the BIF contains between 0.2 and 0.5 wt% MnO. In the massive sulphide rocks magnetite contains _up to 2.3 wt% MnO.

Gahnite Average gahnite endmember composition for the BIF is Ghn70.gHC23.1sSP4.7sGal1.2• Zincian hercynite exsolved from magnetite in non-sulphide-bearing magnetite quartzite has a composition of Hcs 9 • 6 Ghn24.7Spg.sGala.2• In the massive sulphide rock, analysed gahnite has the composition Ghn7s.4Hc1aSPs.3Gal1.3• Gahnite in the amphibole-garnet quartzite has the composition

Ghns2.sHC34.aSP12.s• Figures 9, 10 show variation in wt% FeO and MgO compared to wt% ZnO in gahnite. Gahnite from Dabiepoort has similar composition to the sulphide-associated gahnite at Broken Hill. However gahnite in the garnet-amphibole quartzite from Aggeneys has lower zinc and higher magnesium content than sulphide-associated gahnite. Zincian hercynite exsolved from magnetite in the BIF has a relatively high Fe content. Compositional differences in g~hnite ~ay r~flect variation in bulk rock chemistry and thus available components for gahnite formation or alternatively may reflect a sensitivity of gahnite composition to variation in parameters such as.metamorphic fluid, temperature, pressure or f (0) 2• By accounting for the Fe content of gahnite in these rocks Figure 11 shows that gahnite compositions define separate fields in the different. lithologies and thus show sensitivity to variations in bulk rock chemistry despite the dominantly iron-rich character of the surrounding lithologies at Aggeneys. Analysed gahnite and zincian hercynite from samples studied are plotted on a triangular endmember diagram, Figure 12. Available data on gahnite

-40-

0 c: N

40

30

~ 20 ... ~

10

0

• '": ii.·

Symbols: large dots small dots open squares open triangles:

•

10

• . ••

0

oD 0

0

20

wt% FeO

30

massive sulphide (Broken Hill) gahnite-bearing quartzite (Dabiepoort) garnet-orthoamphibole quartzite (Aggeneys) magnetite quartzite (Broken Hill)

Figure 9: Gahnite compositions, (Broken Hill): ZnO/FeO

-41-

40

• .. :\ .-.. • • .

30 . • •

20

0 c:

N

* ... ~

10-

0 1

Symbols: large dots sma 11 dots open squares open triangles:

0

a° 0 0

0

0 ..

/:),. /:),.

/:),. /:),.

/:),.

2 3 4 5

wt% MgO

massive sulphide (Broken Hill) gahnite-bearing quartzite (Dabiepoort) garnet-orthoamphibole quartzite (Aggeneys) magnetite quartzite (Broken Hill)

Figure 10: Gahnite compositions, (Broken Hill): ZnO/MgO

-42-

-

GI ...... +0·5"' Cl

~ Cl

:::E

0

Symbols: large dots small dots open squares

·open triangles:

o 0 • I I I I I

0·5 Zn/.'. /Zn tfe

"' .... . .. I

massive sulphide (Broken Hill) gahnite-bearing quartzite (Dabiepoort) garnet-orthoamphibole quartzite (Aggeneys) magnetite quartzite (Broken Hill)

Figure 11: Gahnite compositions, (Broken Hill): Mg/Mg+Fe vs. Zn/Zn+Fe

-43-

SPIN EL

Symbols: large dots small dots open squares open triangles:

GAHN I TE

1 .. ;-·,,.,, .

: ~~ I

\ I

'{ 0

1' OJ 1\ 0 I \ o \ I '----D----'\-

1 ', I \ I \ I A \ I \ I A \ I A \ I 2 A \

A I A \

I ' I \ I \ I \ I \ I '

HERCYNIT'E

massive sulphide (Broken Hill) gahnite-bearing quartzite (Dabiepoort) garnet-orthoamphibole quartzite (Aggeneys) magnetite quartzite (Broken Hill)

Field 1: gahnite associated with metamorphosed massive sulphide deposits (Spry, 1984).

Field 2: gahnite associated with aluminous metasediments (Spry, 1984).

Figure 12: Gahnite compositions (Broken Hill) plotted on a triangular

end-member diagram. -44-

associated with sulphide mineralization in other parts of Namaqualand is listed in Table 9, as well as some reported compositions from metamorphosed massive sulphide deposits from other parts of the world. It is apparent that gahnite cbmposition can vary substantially, however, most of those associated with metamorphosed massive sulphide deposits eg. Appalachians (Sandhaus, 1981), Swedish Caledonides (Sundblad, 1982), Quebec (Bernier et al., 1984), Broken Hill, Australia (Plimer, 1977) have high zinc contents and low spinel contents as was suggested by Spry (1984). Included on Figure 12 are the fields proposed by Spry (1984) for gahnite from metamorphosed massive sulphide, deposits (field 1) and from aluminous metasediments (field 2). Table 9 also includes Mg-rich gahnite compositions from high-Mg, aluminous rocks (Essene et al. 1982, Wolter and Siefert 1984, Treloar et al. 1981). Gahnite from the anthophyllite-,garnet-bearing quartzite similarly shows higher Mg contents (11-15 mol% spinel) than the sulphide associated

gahnite (3-6 mol% spinel). The high Zn content of gahnite associated with sulphides (70-80 mol% gahnite), high Mg content of gahnite in the Mg-rich, anthophyllite-,garnet-bearing quartzite and high Fe content of gahnite exsolved from magnetite appear to indicate a sensitivity of spinel composition to bulk rock chemistry.

4.2.3 Metamorphism and f (0) 2

Samples obtained from the metapelitic schist at Broken Hill contain the assemblage: quartz-biotite-sillimanite (+ K feldspar, garnet, magnetite). The BAMM Buffer (Zen, 1985) for oxygen fugacity calculation is applicable to this assemblage and the presence bf co-existing biotite and garnet enable calculation of metamorphic temperature.

Texturally, biotite and sillimanite define a pervasive schistosity in these rocks. Quartz is strained with grains elongate parallel to the fabric defined by sillimanite and biotite. Biotite is orange-brown to pale brown and is partially corroded along the grain boundaries. The association of biotite, sillimanite and garnet suggest a prograde dehydration reactio~ involving biotite as a reactant phase. Garnet grains are small (approximately 1 mm in diameter), and mostly occur as inclusions

-45-

Table 9. Gmnite ~sitions fran Namaqualand, sare massive sulphide deix>sits and M:J-rich rocks.

CCMlOSITIOO OF ~ITE IN ~

Locality: Reference: Asseublage: nol% Gmnite Hercynite Spinel Galaxite

Gamsberg Rozendaal, 1982 B rrerrber (ore zone) 38 58 3 1 C rrerrber (ore zone) 77 18 <5 <1

Kielder District, Q:>rton, 1981 massive sulphide rocks 29 40 31 1 Namaqualand This study 35 11 53 <1 Kol.berg Synform, · Rozendaal 1982 qtz-fsp-sill gneiss 3) 56 13 1

Namaqualand magnetite zones 26 46 20 8

Broken Hill,Black Spry, 1986, massive sulphide 65-85 M:x.mtain; Aggeneys 1987a garnet quartzites 18-75

CCWOSITIOO OF GPJ-WITE IN t-'1ASSIVE SULPHIDE DEPOSITS

Massive sulphide cleJX>sit, Sandhaus, 1981 mineralised netapelitic 70-82 7-24 4-14 Mineral District,Virginia and netavolc:arlic rocks SNedish Caleoonides Suncblad, 1982 mineralised quartz-mica 66-82 15-24 3-10

schists Bleikvassli ore depcisit, Vokes, 1962 quartz-rich rruscovite 79 8 11 2 Norway schist Massive sulphide deix>sit, Bernier et al. biotite-garnet-quartzo- 72 20 8 MJntalben-Les-Mines, Que. 1984 feldspathic gneiss Massive sulphide deix>sit, Pliner, 1977 sulphide associated 57-78 19-38 4-5 Broken Hill, Australia netapelitic rocks Massive-sulphide deix>sit, Wi 11 i ams, 1983 sulphide associated 72 20 8 Fornas, Spain netabasites Archean Iron Formation Awel' 1986 mineralised BIF and 00 26 14

associated anthJphyllite-gedrite rock

CCMlOSITIOO OF ~ITE IN MIGJESIJW-RIQ-1 ROCKS

Massive sulphide deix>sit, Essene et al., spinel-nigerite-hogbcmite 41 3) 29 Manitau.vadge, Ontario 1982 rock Massive sulphide deix>sit, v.blter and cordierite-anthJphyllite fJJ-70 16-00 0-24

' Falun, SNeden Siefert, 1984 rock Cu-Co-Zn' ore bodies Treloar et al., spinel-phlogopite schist 13-15 73-78 8-12 <1 Outokl..ITpll district, 1981 crd-arrphibole rock 23-61 23-70 9-19 <1 Finland

-46-

in biotite. Garnets commonly have a central poikiloblastic region containing tiny quartz and magnetite inclusions and clear rims. In some assemblages biotite is replaced by retrograde chlorite.

Average analysed mineral compositions from the aluminous schist are included in Table 8. The structural formula for muscovite is : K1.24Naa.oe(Fea.2Mgo.07)(Tio.oeAl3.7)SieAl2020(.0H)4 and for biotite is K1.aNaa.03Fe3Mg1.2Ala.7Tio.4(Sis.3Al2.7)02aOH2. The compositional range for garnet is Alm74-79Py3Spess13-20Gross3-4•

Ryan et al. (1982) propose three metamorphic episodes in the Bushmanland rocks at Aggeneys, the first, Ml, is largely masked by re-equilibration during the slightly lower M2 event. Temperatures of 670 - 695 °C and pressures between 3.5 and 6 kbar have been estimated for the observed maximum metamorphic grade attained in the area (M2) (Ryan et al., 1982) . These estimates are based on the presence of orthoclase, sillimanite and cordierite in the aluminous schist, diopside in the amphibolites, and grossular garnet in calc-silicate rocks at Aggeneys. Retrograde metamorphism to greenschist facies, (M3), result in alteration of garnet to chlorite and epidote, sillimanite to sericite • An estimate of 440 °C at similar or lower pressures is given for this event (Ryan et al., 1982).

In order to calculate P-T conditions of maximum metamorphism, (M2), cores of coexisting garnet-biotite pairs were analysed. Cores were selected to minimise the effects of Fe-Mg re-equilibration during (M3) retrograde metamorphism (Indares and Martingole, 1985b). Results of calculations are listed in Table 10 • Biotite-garnet pairs yield a maximum temperature of 650 °C at 4.5 - 5 kbar, according to the method of Indares and Martingole (1985a). An explanation of this method is outlined in Appendix 2. Garnet was found to be significantly spessartine-rich in the rocks studied (13-20 mol% spessartine component).

In the magnetite quartzite, small exsolved grains of green spinel occur. along the borders of the magnetite grains. Both magnetite and hercynite co-exist with quartz in this assemblage. The hercynite-quartz stability field has been investigated by Richardson

-47-

Table 10: Results of geothermometry on co-existing garnet-biotite pairs in a sample of the aluminous schist from Broken Hill.

analysis nr: 1 2

Corrections for substitution in Garnet Xca 0.0330 0.0336 XMn 0.1962 0.1933 Ko=Fe/Mg 12.9167 12.1050

Corrections for substitution in Biotite XT1 0.0761 XA, 0.1195 Ko=Fe/Mg 2.8586

at 5 kbar pressure T°K 915 T°C 643

0.0941 0.1331 2.2000

800 527

Maximum Temperature = 915 °K or 643 °C

-48-

3

0.0332 0.1908 12.5398

0.0899 0.1963 2.6271

843 570

4

0.0313 o·.1922 12.6954

0.0810 0.1218 2.8445

908 635

(1968), Hensen and Green (1971), Holdaway and Lee (1977) and Bohlen et al. (1986). Bohlen et al., (1986) did experimental studies in the Fe-Al 203-Si02 system and determined the equilibrium locus of the reaction: 3 FeAl204 + 5 Si02 = fe3Al2Si3012 = 2Al2SiOs which is located at 5.2 kbar and 865 - 880 °C. However this reaction has a positive dP/dT slope and incorporation of zinc and/or magnetite in hercynite increases the stability field of hercynite-quartz. Zinc,

/

especially may stabilise hercynite to much lower temperatures (Fiost 1973, Vielzeuf 1983). In the magnetite quartzite, hercynite has the

composition HCss-s9Ghn20-3sSPe-11.

Magnetite is able to absorb a limited quantity of zinc into its structure (Wedepohl 1970, Deer et al 1980). The solidus limiting the solid solution between magnetite and hercynite is shown to be dependent on temperature and oxygen fugacity (Turncock and Eugster, 1962). According to their calculated isothermal sections magnetite is able to incorporate less than 5 mol% hercynite in solid solution at 600 °C and f(0)2 = -14. Above 600 °C and at lower f(0.) 2, the solid solution between magnetite and hercynite increases.

The experiments of Turncock and Eugster (1962) show that magnetite­hercynite solid solution is severely limited at amphibolite grades of metamorphism. Similarly, there is a limit to the stability field of hercynite and quartz at amphibolite facies (Bohlen et al., 1986). However the incorporation of a percentage of zinc into the siructure of hercynite may increase the stability field of hercynite-quartz to amphibolite grades and lower (Frost 1973, Vielseuf 1983). In the magnetite quartzite, it is probable that the hercynite-quartz and hercynite-magnetite assemblages coexist by virtue of the zinc content of the original spinel phase. Exsolution of magnetite-hercynite possibly occurred during the post metamorphic cooling stages of the upper amphibolite grade, (Ml), event.

Metamorphic f(0)2

Zen (1985), proposed an empirical calculation for f(0)2 based on the assemblage biotite-garnet-muscovite-magnetite-quartz. The aluminous schist contains this assemblage. Table 11 shows results of calculations

-49-

Table 11: Results of oxygen fugacity calculations on the aluminous schist and BIF from Broken Hill.

Rock Type: BIF

Sample nr: BH-2

Correction: biotite -4 log Xs1 0.15 -3 log xF .. 1.56

Correction: garnet -3 log XFe

Correction: muscovite +2 log XA1 -0.15 +4· log Xs 1 -0.01

Average correction biotite 1. 71

Average correction muscovite -0.13

Average correction garnet 0.91

Total correction 2.47

BHWE-1 BHL0-1

0.91 0.73

Reference BAMM buffer at 650 °c and 4.5 kb:

A luminous Schist

BHG156-7 BHG156-5

0.22 0.20 0.86

0.40

-0.02

1.02

-0.07

0.37

1.30

Log f(0)2 ~ 10.29 - 26284/T + 0.148(P-1)/T ± 650/T = -17.5 ± 0.7

Corrected log f(0)2 Aluminous Schist = -16.02 ± 0.7

-50-

AG80-195

0.24 0.83

0.33

-0.05

employing the BAMM buffer system of Zen (1985) and using the calculated temperature of 650 °C and pressure of 4.5 kb. The BAMM Buffer yields a metamorphic log f(0) 2 of -17.5 +/- 0.7 without correction for substitution for Fe in biotite and garnet and Al in biotite and muscovite. Corrections for the substitutions yield calculated log f(0) 2 = -16.02 +/- 0.7. An attempt was made to apply the buffer to the sulphide-rich BIF, but as the calculation does not take the sulphide phases into account, the results are invalid.

4.2.4 Gahnite Formation

In their study of gahnite at Aggeneys, Spry and Scott (1987a) suggest two reactions for gahnite growth in the sulphide-rich rocks i.e. 1. Fe3Al 2Si3012 (in garnet)+ ZnS + S2 -> ZnAl204 + 3FeS + 3Si02 + 02 2. Fe3Al 2Si 3012 + ZnS + 2.5S2 -> ZnAl204 + 3FeS2 + 3Si02 + 02

in the sulphide~free assemblages, e.g. aluminous metasediments, magnetite­barite rocks, garnet-quartzites and magnetite quartzites, they suggest that gahnite-formed during prograde metamorphism of sulphide-bearing sediments i.e. 3. Al 2Si20s(OH)4(kaolinite) + ZnS + 0.502 -> ZnAl204 + 2Si02 + 2H20 + O.SS2

Gahnite and garnet are observed.in a number of sulphide- and non-sulphide­bearing assemblages, although not necessarily in contact, but evidence of garnet breakdown is sparse. Spessartine-rich garnet, as occurs at Aggeneys, is generally accepted as a variety which is stable at relatively low metamorphic grades. Although not observed in the rocks studied, it is more likely that garnet alters to form chlorite than breaks down in an anhydrous reaction to form gahnite.

Gahnite is associated with muscovite and phlogopite in sulphide-bearing rocks, however, the almost insignificant quantities of zinc in mica limits the possibility of gahnite formation from a precursor zinc-bearing phase (Oietvorst, 1980). The common association of gahnite and sphalerite in sulphide-bearing assemblages suggests that gahnite formed early in the paragenetic history as opposed to forming by retrograde alteration of mica or by garnet breakdown.

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\

Ririe (1982) found that coexisting gahnite-magnetite along with ore minerals, in Precambrian sulphide deposits in Colorado, display metamorphic textures which are consistent with a premetamorphic origin. Evidence supports the formation of magnetite and gahnite during prograde metamorphism in response to changes in f(5)2 and f(Ol2 by the

reactions; 4. 3Fe52 + 202 -> Fe304 + 352

1/202 + Al25i0s + Zn5 -> ZnAl204 + 5i02 + 1/252 At Aggeneys and Gamsberg there is some dispute as to the origin of the sulphide mineralization with support for a fumarolic exhalative source (Ryan et al., 1982 and Rozendaal, 1982) and a chemogenic sedimentary origin (Moore 1986). It would appear from the metamorphic textures observed in this study that gahnite, sphalerite and magnetite formed during th~ same prograde metamorphic event and are thus premetamorphic in

origin.

Moore and Reid (1988, in press) show that gahnite associated with sphalerite in quartzites in Namaqualand can form from infiltrating metamorphic fluids carrying alkali-Al203 complexes e.g. 5. 2KH2 + (Zn,Fe)5 -> (Zn,Fe)Al204 + H25 + 2KOH or at lower K+/H+, 6. 2H3Al03 + (Zn,Fe)5 -> {Zn,Fe)Al204 + H20 + H25. A similar hydrothermal-type reaction was proposed by Hobbs (1975) for gahnite formation in pegmatities and quartz veins at Broken Hill massive

sulphide deposit, Australia. The presence of muscovite rims around gahnite in some rocks appears to support the introduction of a fluid phase into the rocks, possibly associated with the later, retrograde metamorphic event (M3) in this area. The stability of gahnite at amphibolite grades of metamorphism (650 °C, 5 kbar) is indicated by its coexistence with sphalerite, garnet and quartz in sulphide-bearing assemblages. It is therefore suggested that gahnite-formation was initiated during diagenesis and continued during prograde metamorphism of the sulphide-bearing sediments. A reaction such as (3), above is envisaged during diagenesis and d~ring the early metamorphic stages. The abundance of micas and garnet in the rocks indicate an adequate supply of Al throughout the metamorphic paragenesis.

-52-

Subsequent to the Ml and M2 metamorphic events, low grade metamorphism accompanied by the introduction of K-bearing fluids into the rocks would account for retrograde breakdown of phlogopite and formation of muscovite in some of the assemblages observed. Reactions such as (5) and (6) are possibly associated with the retrograde event. The presence of sulphides

' and ubiquitous K-bearing mica phases, in the halo of rocks which surround the ore bodies at Aggeneys, indicate .an adequate supply of Zn and K for this type of reaction.

-53-

4.3 ACHAB

4.3.1 Petrography

Gahnite-bearing quartzites can be traced as a thin horizon in the aluminous schist from the Namiesberg mountain on Achab farm northwards beyond Tafelberg and towards the Gamsberg in the northwest (Fig.5). In the Namiesberg, gahnite occurs mostly in quartzites and schists at the contact of the aluminous schist and the underlying quartzo-feldspathic gneiss. Gahnite occurs locally in the upper horizons of the aluminous schist at its contact with the metaquarzite unit.

Metapelitic Rocks

Metapelitic rocks sampled for the study of gahnite at this locality include sillimanite and muscovite schists, a cordierite-gedrite rock and biotite-sillimanite-muscovite schists. Gahnite is present in the biotite-sillimanite-muscovite schist which also contains minor ilmenite and rutile. The sillimanite and muscovite schists sampled are almost monomineralic, containing only accessory· quantities of zircon. Table 12 lists modal proportions of minerals present in the rocks studied.

Gahnite-bearing biotite-muscovite-sillimanite schists are composed of coarse red-brown biotite, muscovite and fibrolite {Fig.13). Abundant tiny inclusions of zircon occur in coarse biotite laths. Biotite, muscovite and gahnite, sillimanite {Plate 1) or garnet form the major phases present in these rocks (Table 12). Garnet occurs as coarse, euhedral porphyroblasts with a central portion.containing many minute quartz inclusions. Occasional grains of biotite and rare green gahnite also occur as inclusions in garnet. Anhedral green gahnite is found interstitially to biotite, sometimes bordering on garnet grains and contains both biotite and sillimanite inclusions (Plate 2). Gahnite occurs as a prograde mineral in these assemblages. No Fe-Ti oxides are present in these samples, although they occur in most other lithologies at this locality.

-54-

/

Figure 13:

/mm L----1

Textural relationship of gahnite in the biotite-muscovite­schist.

-55-

Table 12. Estimated rrodal proportions of minerals present i~ sam::iles studied at Achab.

SPWLE ABN 1 ABN 5 ABN 2 ABN 4 ABN 16 ABN 6

Quartz 10 65 15 Biotite 65 15 m Garnet 15 35 Cordierite tr m Sillimanite 85 25 m 35 Plagioclase tr M...lscovite m 95 15 35 Seri cite m Magnetite tr 10 tr m Gahnite tr 15 Rutile m Zircon tr tr Gedrite 40 Tourmaline

SAfvPLE ABN 3 ABN 8 ABN 9 ABN 10 ABN 11 ABN 12

Quartz 95 00 00 00 90 75 Biotite m m m 10

·Garnet Cordierite Sill imanite 10 m Orthoclase M.lscovite tr tr Sericite tr tr tr

·Magnetite m tr m tr tr m Gahnite tr 20 10 5 10 10 Rutile tr tr tr tr Zircon

'm' indicates minerals present in minor proportions (5% or less) 'tr' indicates minerals present in trace quantities (1% or less)

ROCK TYPE

ABN 1,5 ABN 2 ABN 4,16 ABN 6 ABN 7 ABN 3,8-15

sillimanite schist nuscovite schist biotite-tn.iscovite-sillimanite(+garnet, gahnite) schist garnet-gedrite rock tourmaline quartzite gahnite quartzite

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ABN 7

00 tr

40

ABN 13 ABN 14 ABN 15

85 85 95 tr tr

m

tr tr tr 10 15 tr tr tr

I The porphyroblastic garnet-gedrite rock has a matrix composed of quartz and minor cordierite, plagioclase and biotite. Porphyroblasts of gedrite contain inclusions of biotite, quartz, magnetite and cordierite and are bordered by biotite and cordierite. Garnet porphyroblasts contain quartz and magnetite·inclusions and are generally surrounded by biotite. Garnet and gedrite comprise in excess of 70 % of constituents of this rock. Rare grains of green zincian spinel are associated with magnetite as inclusions

in gedrite.

Gahnite-bearing Quartzites

The gahnite-bearing quartzites contain 5-20 modal% gahnite in a coarsely crystalline quartz martix (Table 12). In some rocks vughs are associated with gahnite-rich laminae. The vughs may be partially infilled with rutile and goethite •. The possibility that the vughs are dissolution features resulting from desulphidation of sulphides appears to be supported by trace element analysis. Up to 1.03 wt% Pb and 522 ppm Cu were found in whole rock analyses of some of the gahnite-quartzites. Gahnite in the laminae occurs as coarse, poikiloblastic porphyroblasts concentrated and aligned along bedding planes (Plate 3). Abundant crystallographically orientated inclusions of quartz give the gahnite porphyroblasts a sieve-like appearance. Small, rounded grai~s of rutile and ilmenite also occur throughout the matrix. In some rocks, gahnite porphyroblasts are associated with cracks and fissures.

Biotite, rutile and muscovite or sillimanite occur as minor phases in the gahnite quartzites (biotite and sillimanite locally up to 10%). Rutile occurs as rounded grains and is closely associated with gahnite. Gahnite-biotite and or gahnite-muscovite associations are fairly common and occassionally rare gahnite grains contain inclusions of needle-like sillimanite. In many of the gahnite quartzites, gahnite is associated

with prograde muscovite and biotite.

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4.3.2 Mineral Chemistry

The bulk compositions of metapelitic schists and quartzites from this locality indicate high Si, Al and Fe contents and low Mg and K contents (Table 13). Figure 14 gives an indication of the relative proportions of these elements. Relatively high Ti contents (1.3 - 4.9 wt%) are attributed to the presence of trace quantities of ilmenite and minor rutile in the quartzites. Zr contents of 300 - 1300 ppm are attributed to, the presence of abundant zircon inclusions in biotite in the metapelitic schists. Significant quantities of Rb (up to 450 ppm) are similarly associated with biotite in the schists. The presence of zinc, in the quartzites is attributed to gahnite. Pb contents of 1.03 wt% and Cu up to

, 522 ppm have been attributed to trace quantities of sulphides (now oxidised) in the quartzites.

Average analyses of minerals in the samples studied are given in Table 14.

Garnet, Plagioclase and Cordierite

The biotite-muscovite-sillimanite schist and the cordierite-anthophyllite rock contain garnet in their assemblages. Endmember garnet compositions are plotted on Figure 15. Average garnet composition in the schists is; Alm70.sPYa.sSpess22Gross3. In the porphyroblastic garnet-gedrite rock garnet, co-existing with Mg-rich cordierite and gedrite, has the composition; A1m77.ePY13.sSpessa.eGrossa. The composition of plagioclase in this rock is AnaeAbs1•

Biotite and Muscovite

Biotite compositions have been plotted on an endmember diagram {Fig.16) and are shown to be fairly Al-rich (siderophyllite}. In zinc-rich lithologies, micas commonly incorporate zinc into their structure (Palache 1935, Frondel and Ito 1966, 1975, Plimer 1977, Stern and Klein 1983). In gahnite-bearing quartzites at Achab muscovite contained less than 0.02 wt% ZnO (lower detection limit= 0.02). However, biotite has ZnO contents of 0.06 - 0.16 wt% and locally up to 0.28 wt%. An altered biotite grain in one of the gahnite quartzites contained 0.7 wt% ZnO. In gahnite-bearing schists biotite contained up to 0.35, wt% ZnO and in the porphyroblastic garnet-gedrite rock 0.09 wt% ZnO.

-sa~

\

Table 13. Wl:>le rock analyses of sane quartzites and iretapelitic schists from Achab.

(analyses by generosity of Dr. J.M. MJore).

Sartple: ~1 AEW-2 AE!N-3 ABN-4 ABN-5 ABN-6 AE!N-7 ABN-8 ABN-9

Si02 40.67 71.47 95.10 36.33 64.37 49.96 78.00 82.66 74.04 Ti02 2.04 0.87 0.04 -1.29 4.85 3.51 0.41 0.41 2.29

Al203 54.26 18.91 1.23 36.22 23.74 16.49 11.82 7.85 5.62

FeO 0.89 0.62 2.44 12.95 5.42 14.62 ·2.65 3.34 9.10 Mi) 0.00 0.00 0.00 0.72 0.12 0.36 0.00 0.00 0.13 Mj) 0.00 0.00 0.24 3.37 0.21 7.34 2.10 0.00 0.18

CaO o.a> 0.02 0.02 0.39 0.67 1.91. 0.33 0.03 0.32

Na20 0.28 0.35 0.03 0.14 0.25 0.55 0.40 0.14 0.13

K20 1.54 4.33 0.41 5.02 0.13 1.52 0.10 0.00 0.40

P205 O.C6 0.03 0.02 0.24 0.43 1.17 0.00 O.C6 . 0.55

H20+ 1.:£> 3.C6 0.56 3.59 0.61 2.53 1.65 0.54 4.34

H20- 0.10 0.13 0.02 0.16 0.02 0.11 -0.01 0.02 0.10

Total 101.29 99.65 100.00 100.26 100.00 99.96 97.46 95.10 97.10

Trace elerrents (pµn) Rb 76 178 38 457 12 123 5 8 17

Ba 83 583 82 249 112 556 12 88 276

Sr 34 67 2 15 27 31 29 5 115

Th 41 21 <4 37 5 6 10 39 348

u 5 4 <3 5 <4 <5 <3 5 <5

Zr 1310 001 45 739 369 290 384 500 221 l\t> 62 20 2 58 26 18 14 9 5

~ 1 <1 <1 5 4 5 <1 43 78

Sc 28 11 0.8 37 24 25 7.8 4.6 11

Ni 2.3 1.9 7.2 38 3.8 17 24 <2 <2.4

Pb 22 34 <5 26 75 97 9 9 1.03% Zn 39 3.5 218 173'.) 182 598 76 3.2% 1.33% Cu 1.9 <1.1 19 16 38 <2 <1 70 522 y 33 12 <2 70 32 46 16 22 25 La 43 28 <2 38 39 19 6.2 19 16

Ce 96 61 7 92 103 69 17 44 51 Nd 44 27 <3 41 63 46 8.7 19 3'.)

-59-

FeO

Figure 14:

FeO+MgO

0

• •

FeO+MgO

MgO

Whole rock compositions of some samples from Achab plotted on triangular diagrams.

-60-

'·.:

Table 14. Average (or Representative) analyses of minerals studied in Achab rocks.

Gl\RNET CORDIERITE Pl..PliIOCLASE GEOOITE SILLirvwJITE

n 18 14 6 3 2 1 SJMlLE ABN 4 ABN 6 ABN 6 ABN 6 ABN 6 ABN 16

cf (j' Cf () 6 Si02 35.89 0.62 37.00 0.54 48.98 0.28 55.66 0.49 43.13 0.84 36.14 Ti02 0.01 0.01 nd nd nd 0.23 0.00 nd Al203 21.42 0.25 21.65 0.45 32.97 0.15 27.48 0.31 15.75 0.47 62.67 FeO '.n.45 1.26 32.52 1.20 6.00 0.22 n"d 23.76 0.05 0.34 r.\10 9.51 1.56 2.07 0.36 0.11 0.05 nd 0.55 0.03 nd M30 1.94 0.37 5.64 0.63 9.81 0.00 nd 13.33 0.00 nd CaO 1.29 0.44 1.66 0.11 nd 0.40 9.50 0.40 0.52 0.00 nd ZnO nd nd nd nd 0.00 0.00 nd Na20 nd nd 0.35 0.05 5.93 0.20 1.72 0.02 nd K20 nd nd nd 0.04 0.00 - nd nd

Total 100.51 100.62 98.:n 98.61 99.00 99.15

BIOTITE

Nr.anal. 4 4 9 4 5 2 S!MlLE ABN 3 ABN 4 ABN 6 ABN 9 ABN 10 ABN 13

rf () r1 cr O' cr Si02 36.05 1.23 34.55 0.05 37.15 0.55 35.42 0.43 35.66 0.74 36.65 0.65 Ti02 0.78 0.03 2.22 0.23 1.29 0.18 2.17 0.74 3.10 0.66 3.14 0.18 Al203 20.62 o.ro 21.00 2.74 17.69 0.25 18.57 0.32 19.53 0.31 19.87 1.10 FeO 18.34 1.20 21.03 1.19 14.69 0.47 14.12 0.50 20.22 0.85 18.59 0.02 ~ 0.29 0.00 0.26 0.00 nd 0.15 0.05 0.29 0[05 0.28 0.03 M:30 8.17 1.31 7.82 0.62 15.32 0.28 12.90 0.98 9.00 0.77 6.92 0.37 CaO nd nd nd nd nd nd ZnO 0.16 0.01 0.10 0.00 o.oo 0.01 0.05 0.07 0.13 0.00 nd Na20 0.23 0.00 0.28 0.04 0.42 0.05 0.40 0.04 0.31 0.03 0.22 0.00 K20 7.90 1.45 . 8.43 0.59 7.79 0.46 7.95 0.13 8.97 0.00 7.72 0.13

Total 92.55 95.69 94.44 91.74 97.21 93.39

nd: element was not detected or the anount detected was belo.v the detection limit of the analytical method enployed. 6: is a statistical measure of 'n' number of analyses All Fe is analysed as FeO.

Table 14. Average (or Representative) analyses of minerals studied in Achab rocks.

' BIOTITE MJSCOVITE

n 5 1 3 1 1 2, SolvPLE ABN 16 ABN 1 ABN 2 ABN 4 ABN 12 ABN 16

d <f 6 Si02 34.13 0.25 44.28 43.84 0.61 45.51 43.59 45.14 0.17 Ti02 3.33 0.22 1.71 1.74 0.04 0.66 1.76 1.16 0.11 Al203 19.32 0.23 35.73 34.90 0.26 37.14 34.53 36.47 0.86 FeO 22.81 o.ro 0.95 1.25 0.15 2.10 . 0.92 1.37 0.18 r-\'10 0.23 0.03 nd nd O.aJ nd nd Mt> 6.77 0.15 0.56 0.58 O.aJ 0.69 0.64 . 0.49 0.01 eao nd nd nd nd nd nd ZnO 0.12 0.17 nd nd nd nd 0.02 0.00 Na20 0.22 0.02 0.00 0.59 0.02 0.52 0.54 0.67 0.01 K20 8.53 0.11 9.24 9.07 0.07 8.3) 9.05 10.16 0.12

Total 95.46 93.27 91.97 94.98 91.03 95.48

OOf\IITE

n 6 5 2 11 3 4 SA"IPLE ABN 3 ABN 4 ABN 6 ABN 8 ABN 9 ABN 10

6 c{ 6 <f 6 Al203 55.42 0.47 56.13 0.37 56.83 0.36 56.aJ 0.27 58.33 0.52 55.79 0.26 Cr203 nd 0.29 0.11 nd 0.04 0.05 nd nd FeO · 15.18 1.87 13.48 2.13 22.68 1.58 9.65 0.21 13.82 0.29 11.25 2.45 l'-\'JO 0.38 0.12 0.32 0.04 0.14 0.01 0.20 0.04 0.31 0.03 . 0.36 0.05 Mg() 2.15 0.24 1.21 0.22 6.27 0.72 1.36 0.03 3.62 0.24 1.98 0.18 ZnO 25.46 2.15 28.3) 2.54 13.22 1.91 32.83 0.21' 24.67 0.38 3).16 2.88

1'.'· .:j: ' i '·' . Total 98.59 99.73 99.14 100.14 100.75 99.54 { •'. ,r

'~ _!'

o:. nd: elerrent was not detected or the arrount detected was belo,y the detection \" c- , .. ,

limit of the analytical rretrod errployed. , ....• 6: is a statistical rreasure of 'n' nl.llber of analyses All Fe is analysed as FeO

'-~ ' I!

,. '

-62-

/

Table 14. Average (or Representative) analyses of minerals studied in Achab rocks.

GAHNITE

n 13 4 7 7 8 SoWLE ABN 11 ABN 12 ABN 13 ABN 14 ABN 16

d 6 6 6 <f Al203 56.54 0.42 57.20 o.~1 56.91 0.29 59.01 0.98 56.50 0.53 Cr203 nd 0.11 Ofl 0.04 0.05 0.02 0.04 0.06 0.05 FeO 15.00 1.02 12.24 0.26 13.41 1.CO 10.27 0.34 14.93 0.20 ~ 0.26 0.03 0.20 0.103 0.42 0.03 0.3'.) 0.03 0.26 0.04 tJgO 1.45 0.14• 2.04 0.04 1.74 0.03 1.65 0.03 1.41 0.14 ZnO 25.94 0.98 27.86 o. 28 27.21 0.52 29.61 0.52 26.87 0.23

Total 99.27 99.65 99.73 lC0.86 100.03

nd: eleirent was not detected or the arrount detected was belON the detection limit of the analytical rretroo e~lqyed. d: is a statistical rreasure of 'n' nl.8Tber of analyses All Fe is analysed as FeO

-63-

Figure 15:

SPESSARTINE

GROSSULAR

Symbols: open squares garnet-gedrite schist open triangles: biotite-muscovite-sillimanite schist

Garnet compositions (Achab) plotted on a triangular endmember diagram.

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ANNITE SIDEROPHYLLITE

. . . -, I

.

.

. ~----- ----------------

'PHLOGOPITE EASTON I TE

Figure 16: Biotite· combositions (Achab) plotted on an endmember diagram.

-65-

\ \

\

GAHNITE

\ \

1

\ / ... ,~, 'i I(~\

\ \ I \ \ I \ :• • \ I \ •. \ I '--------,-\ \ I \ I I I I

D\ I I I I I I I

a

2

\ \

\ \

\ \

\ \

\ \

\ \

\ \

\

SPINEL HERCYNITE

Symbols: dots open circles open triangle~: open squares

gahnite quartzites biotite-muscovite-sillimanite-gahnite schist biotite~muscovite-garnet-sillimanite schist garnet-gedrite schist

Field 1: gahnite associated with metamorphosed massive sulphide deposits (Spry, 1984).

Field 2: gahnite associated with aluminous metasediments (Spry, 1984).

Figure 17: Gahnite compositions (Achab) plotted on a triangular endmember ' diagram.

-67-

40

30

0 c: 20 N

cf!. ...... ~

10

0

. '\ • • ••

Symbols: dots open circles open triangles: open squares

£j_gure 18:

-rf-!~ s. el&. •• •

•

0

0

10 20 30

wt%. FeO

gahnite quartzites biotite-muscovite-sillimanite-gahnite schist biotite-muscovite-garnet-sillimanite schist garnet-gedrite schist

Gahnite compositions (Achab~, ZnO/FeO.

-68-

0 c N.

Symbols: dots

30 • • ,

• ~ .. ~:· ,.,..

0

• •

• 04

D

0

10 L----'---1---'----'--'---'-----''"----'---'----"

1 5 wt% MgO

open circles open triangles: open squares

gahnite quartzites biotite-muscovite-sillimanite-gahnite schist biotite-muscovite-garnet-sillimanite schist garnet-gedrite schist

Figure 19: Gahnite compositions (Achab), ZnO/MgO.

-69-

Qj

u.. 0·5

+ Cl

:!: ~ ~

Symbols: dots

0

...

..

open circles open triangles: open squares

I

0 0 ~

' 0·5

Zn/ /Zn +Fe

'

,~ahnite quartzites ~iotite-muscovite-sillimanite-gahnite schist ~iotite-muscovite-garnet-sillimanite schist 4arnet-gedrite schist

Figure 20: Gahnite compositions (Achab), Mg/Mg+Fe vs. Zn/Zn+Fe.

I

...

UJ I-

I-0 Ill ...

~ 0·5

+ Cl • :!: ~·

l . Cl

:!:

..

0

Figure 21:

I

• • I

•• ••

I

I

0·5

Mg/' '/Mg+ Fe

I I '

.

GAHNITE

ratios of biotite:gahnite, (Achab).

-70-

5 - 3 kbar pressure. Sillimanite is stable throughout the Ml and M2 events. The M3 event is characterised by sericitization and chloritization of feldspars and sillimanite. Moore (1977) estimates that greenschist grade metamorphism with temperatures below 500 °C and pressures below 3 kbar existed during the M3 metamorphic event.

Assemblages observed in the metapelitic rocks at Achab include; Biotite +muscovite+ garnet (+ sillimanite, gahnite) Sillimanite +muscovite+ biotite + gahnite Garnet+ gedrite +quartz+ biotite + cordierite + plagioclase (+ilmenite, magnetite, hercynite) Sillimanite +quartz·+ rutile +ilmenite Muscovite + sericite + rutile + ilmenite

The reaction determining the transition from medium to high grade metamorphism i~ metapelitic rocks is; muscovite+ biotite +quartz= K-feldspar + aimandine + sillimanite + H2 0 (Winkler, 1967). This takes place at around 640-650 °C at between 3.5 and 5 kbar (Winkler op. cit.). The association of biotite, muscovite, sillimanite, almandine and/or gahnite in the pelitic schists indicates that metamorphic conditions close to this transition were reached at this locality.

In the metapelitic biotite-muscovite-sillimanite schists, garnet contains in excess of 20 mol% spessartine indicating possible re~equilibration (during M2 metamorphism) and making it unsuitable for geothermometric calculations. However, the garnet-gedrite rock contains the assemblage: quartz + plagioclase + biotite + cordierite + garnet or gedrite. The presence of plagioclase confirms this assemblage as part of Moore's (1977)

. upper amphibolite grade facies. This is plotted on an AFM diagram (Fig.22). Garnet-biotite pairs from the garnet-gedrite rock were analysed to determine metamorphic temperatures. Garnet contains approximately 80 mol% almandine in this assemblage. Geothermometry by methods of Holdaway and Lee (1977) and Ferry and Spear (1978) indicate a maximum calculated temperature of 670 °£ at 4.5-5 kbar pressure (Table 15). Results employing the method of Thompson (1976) are consistent with those using a. recent method by Indares and Martingale (1985a) whicf1 takes into account substitution of Ti and Al in biotite and Ca and Mn in garnet. Table 15

-71-

F

Figure 22:

A

+ quartz

+ k-fe/dspar

GARNET

BIOTITE

M

Mineral compositions in the garnet-gedrite schist (Achab), plotted on an AFM diagram (Thompson, 1976).

-72-

Table 15: Results of garnet-biotite geothermometry on pelitic rocks

from Achab.

Method Employed

Holdaway & Lee (1977)

Thompson (1976)

Ferry & Spear (1978)

Indares & Martingole (1985a)

Calculated Temperature at 4.5.kbar

garnet-biotite (5 mineral pairs)

669°C

J65'C

L6°C

s60°c

-73-

garnet-cordierite (5 mineral pairs)

638°C

I

lists results of the calculations. The calculated temperature employing the latter method is 560 °C at 5.5 kb indicating re-equilibration during Moore's (1977) M2 event. The former temperature appears to be more compatible with the observed assemblage and is·preferred as an indication of the highest temperature attained during metamorphism of the rocks •

. Oxygen fugacities were calculated using the BAMM buffer proposed by Zen (1985). Results of calculations on prograde assemblages in the metapelitic schists and quartzites show that relatively oxidising conditions were associated with the M2 metamorphic event, i.e. log f(0) 2 = -15.8 to -16.4 at 670°C. Table 16 lists results of the calculations.

4.3.4 Gahnite Formation

Gahnite is associated with biotite, sillimanite and garnet in the schists and biotite and muscovite in the quartzites at Achab. No disequilibrium features are observed between gahnite and quartz. It appears that gahnite is stable in the assemblage observed.

Dietvorst (1980) found that small qu~ntities of gahnite formed by breakdown of zinc-bearing biotite (0.14 - 0.24 wt% ZnO), sillimanite and cordierite to form cordierite and spinel. At Achab, biotite contains up to 0.7 wt% ZnO in some cases, but the large quantities of gahnite in these rocks (up to 15%) and the absence of evidence for biotite breakdon preclude gahnite formation by this method alone.

Small quantities of Pb and Cu were found in whole rock analyses of the quartzites and as Gamsberg is situated only 8 km north-west of the sampling locality, it seems piobable that the rocks at Achab contained sulphides in their precursor sediments. The gahnite-bearing quartzite horizon appears to be correlated stratigraphically with the sulphide-bearing quartzites which underly the ore horizons at Gamsberg (Moore, pers. comm.). A reasonable method of gahnite formation would be that it formed from ZnS-bearing sediments (shales) along with prograde biotite, sillimanite and garnet during the high grade metamorphic event. It is proposed that zinc entered the structure of biotite during prograde

-74-

Table 16: Results of oxygen fugacity calculations on Achab rocks.

Metapelitic Rocks

Assemblages:

(i) Biotit~ +muscovite+ 'arnet + sillimanite + gahnite +ilmenite+ rutile (ii) Cordierite + plagiocla~e + biotite +garnet+ anthophyllite +ilmenite

Sample nr: ABN-4 l ABN-16 ABN-6 ABN-2 ABN-1

Corrections for substitutioi in Biotite -4 log Xs 1 0.22 0.23 0.15 -3 log XFa 1.02 0.93 1.56

Corrections for sub st i tut i 01 in Garnet -3 log XFe /

0.47 0.37

Corrections for substitutio in muscovite +2 log XA, -0.04 0.14 -0.08 +4 log Xs 1 0.01 0.15

Tot,a l correction 1.66 1.16 2.08 0.30 -0.12 Average Correction = 1. 75

Refe~ence BAMM buffer at 67 °C and 5.5 kbar: Log f(0) 2 = 10.29 - 26284/T + 0.148(P-1)/T ± 650/T = -17.58 ± 0.7

Corrected log f(0) 2 = -15.8 ± 0.7

Quartzites

Assemblage:

Quartz + gahnite + s i 11 iman ite + biotite + muscovite + rutile

Sample nr: ABN-3 ABN-12 ABN-9 ABN-10 ABN-13

Corrections for substitution in Biotite -4 log Xs1 0.17 0.18 0.25 0.13 -3 log XFe 1.03 1.56 1.01 1.21

Corrections for substitution in muscovite +2 log XA, -0.08 -0.06 +4 log Xs1 -0.01 -0.01

Total correction 1.20 -0.07 1. 74 1.26 1.29 Average Correction = 1. 21

Reference BAMM buffer at 6~0 °C and 5.5 kbar: Log f(0) 2 = 10.29 - 26284/1+0.148(P-1)/T ± 650/T = Corrected log f(0)2 = -16.37 ± 0.7

-17.58 ± 0.7

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metamorphism. Dietvorst (1980 and Plimer (1977) document prograde biotite, associated with mineralization, containing small quantities of zinc. Dietvorst (op. cit.) found that gahnite formed as a reaction product of the breakdown of biotite to chlorite during retrograde metamorphism. Evidence of Fe-Mg exchange between gahnite and biotite (Fig.21.) is interpreted to result from Zn-Fe-Mg exchange initiated by overstepping the zinc saturation level of biotite during subsequent low grade metamorphism (Moore's M2 event).

Thus initial gahnite formation is the same as that which is suggested at Aggeneys i.e.; ZnS + Al 2Si20s(OH)4 (kaolinite in argillaceous sediments) + 0.5 02 -> ZnAl204 + 2Si02 + O.SS2 + H20 •••• (Spry, 1987a).

In the garnet-gedrite rock small quantities of gahnite occur as inclusions in the gedrite porphyroblasts. Williams (1983) proposed that gahnite formed as inclusions in gedrite associated with sphalerite by reaction; gedrite + sphalerite + 02 -) gahnite + Si02 + H20 (+ S in fluid). However there is no evidence of gedrite breakdown to form gahnite in the garnet-gedrite rock. It would seem thus, that gahnite in this assemblage has also formed as a prograde mineral. The relatively Mg-rich, Zn-poor composition (Fig.17) of gahnite in this assemblage is attributed to the bulk chemistry of the rock in which it formed.

In some of the gahnite quartzites, poikiloblastic gahnite occurs along fractures. It appears that the fractures or cracks acted as conduits whereby fluids carrying the components necessary for gahnite formation could enter the rock. Although biotite is commonly altered in these rocks it is not necessarily associated with fractures (or gahnite) and the biotite breakdown is interpreted to result from a weathering process. Moore and Reid (1988 in press) have suggested that aluminium may be carried in alkali complexes by metamorphic fluids. It is proposed that retrograde breakdown of prograde aluminous mineral phases in_ the underlying sediments resulted in fluids carrying Al-alkali and Zn-Fe oxide complexes which permeated the overlying rocks i.e.; 2KH2Al03 + (Zn,Fe)O + 0 -> (Zn,Fe)Al204 + 2H20 + 2KOH ••• (Moore and Reid, 1988 in press). This resulted in re-equilibration and addition to pre­existing gahnite and accounts for some of the variation in gahnite composition observed at this locality (Fig.17).

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4.4 SWARTKOPPIES

Massive gahnite and porphyroblastic fibrolite-gahnite rocks occur in the economically exploited, sillimanite-corundum rocks at Swartkoppies, on the farm Pella Mission in northern Namaqualand (Fig.1). The regional geology of this locality is described in chapter 3.3.3.

4.4.1 Petrography

Gahnite-bearing rocks from Swartkoppies include a massive, crystalline gahnite rock, a porphyroblastic gahnite-fibrolite rock, a gahnite­fibrolite rock and a gahnite-sillimanite rock. Modal proportions of the minerals present in the samples studied from this locality are listed in Table 17.

The massive gahnite rock is composed almost entirely of medium grained, dark, blue-green, crystalline gahnite. Gahnite grain size is bimodal, with the majority of grains euhedral to subhedral and between 0.5 and 3 mm in size. In patches gahnite is subhedral to anhedral and fine grained (0.1 mm), (Plate 4). Round, 0.4 mm, vugh-like structures infilled with rutile needles and corundum occur throughout. Rutile occasionally forms small, 0.1 mm, reddish-brown inclusions in gahnite. Much of the coarser gahnite grains are colour-zoned with darker green cores and pale, almost colourless rims (Plate 4). Locally yellow~orange goethite infills intergranular spaces and crosscuts gahnite grains.

The porphyroblastic fibrolite-gahnite rock contains isolated, 3.5 - 8 mm, dark green, euhedral gahnite crystals in a massive white fibrolite matrix (Fig.23a). Fibrolite comprises in excess of 90% of this assemblage. Gahnite porphyroblasts contain inclusions of corundum, occasional goethite blebs and fine, needle-like fibrolite. Crystalline gahnite comprises approximately 5% of the rock's constituents. Pale muscovite commonly borders gahnite grains and similarly to gahnite, contains inclusions of fibrolite. Goethite and fine grained rutile occur as minor constituents associated with recrystallized, coarse sillimanite in the matrix. Rare, fine quartz veins transect this rock.

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Table 17. Estimated modal proportions of minerals present in samples

studied from Swartkoppies.

SAMPLE SK 2 SK 10 SK 3 SK 4

Sillimanite 95 70 70 Gahnite 95 m 15 25 Biotite 10 m Rut il e m m m Goethite m Corundum tr Ilmenite 5

'm' indicates minerals present in minor proportions (5% or less). 'tr' indicates minerals present in trace quantities (1% or less).

ROCK TYPES:

SK 2 SK 10 SK 3 SK-4

Massive gahnite rock Porphyroblastic fibrolite-gahnite rock Sillimanite-gahnite-biotite rock fibrolite-gahnite rock

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Figure 23:

tmm ,_____,

b. Reiationship of gahnite to sillimanite and biotite in the sillimanite-gahnite-biotite rock.

Imm L---1

a. Anhedral gahnite porphyroblasts in the fibrolite-gahnite rock.

Abbreviatio s: B - biotite, M - magnetite, G - gahnite, S - sillimanite .

. Textural elationships of gahnite in samples from Swartkoppie

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A sillimanite-gahnite-biotite rock has a matrix composed of recrystallised radiating sillimanite laths and fibrolite. This rock contains approximately 70 mol% sillimanite and 15 mol% gahnite (Fig.23b). Biotite is the only other major mineral phase and comprises approximately 10% of the rock. The presence of sillimanite crystals along with fibrolite probably indicates recrystallization in response to changing metamorphic conditions. Gahnite aggregates are composed of 0.06 - 0.4 mm, subhedral, bright green grains associated with the coarsely crystalline sillimanite. Anhedral gahnite and magnetite blebs also occur as numerous inclusions along cleavage planes in sillimanite (Fig.23b). Locally biotite rich areas occur in the matrix. The biotite is orange-brown to pale brown and similar to sillimanite, contains inclusions of gahnite and magnetite. Biotite grains are interrupted and broken up by the coarse sillimanite laths~ Larger gahnite grains also contain segments of disrupted biotite laths. Magnetite occasionally occurs as coarse 0.6 mm grains associated with gahnite but no gahnite exsolution is observed in magnetite. Minute grains of rutile occur in association with magnetite. It appears that biotite, sillimanite, magnetite, gahnite and rutile have crystallized as part of the same prograde assemblage.

The fibrolite-gahnite rock is composed of fibrous sillimanite and aggregates of gahnite grains. In contrast to the previous lithology, this rock contains very little biotite and fibrolite is not recrysallized to form sillimanite. Gahnite aggregates are composed of 0.1 - 0.4 mm, 'fractured, gahnite grains. Common sillimanite and magnetite inclusions and rare orange-brown biotite occur in the aggregates. Occasional rutile grains are associated with magnetite and spinel. Veins composed of fine grained, polygonal quartz transect the rock. Some of the coarser gahnite grains are colour zoned similar to the massive gahnite rock. No spinel exsolution was observed in magnetite.

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4.4.2 Mineral Chemistry

Mineral analyses of biotite and gahnite are given in Table 18.

Biotite Biotite is annite with approximately 17 wt% FeO and 10 - 13wt% MgO. Average biotite composition (Table 18) is : Ki.sNaa.1Mg3Fe2Alo.a(Sis.3Al2.7)02aOH)4. The zinc content in biotite is below the detection limit of the microprobe for this element (0.02 wt%).

Qualitative analysis for zinc in magnetite and fibrolite similarly indicated a concentration level below the detection limit of the microprobe.

Gahnite In the samples studied gahnite exhibits a marked range in Zn-content considering the small sampling area. Compositions vary between 0.13 -0.35 wt% MnO, 1.7 - 3.5 wt% MgO, 15.7 - 25 wt% FeO, 13.2 - 25 wt% ZnO, and range from zincian hercynite to gahnite •.

Molecular proportions of Zn, Fe and Mg in gahnite were recalculated as end-member gahnite, hercynite and spinel. The normalised values are plotted on a triangular diagram (Fig.24). The galaxite molecule is insignificant (< 0.4 wt% MnO) and is not included.

Gahnite compositions vary from a zincian hercynite in the sillimanite­gahnite-biotite ~eeks to gahnite in the massive gahnite rock and porphyroblastic fibrolite-gahnite. rock. All spinel compositions plot on

' the Fe-rich (hercynite) side of the diagram and show very limited variation in Mg content. The compositional range of gahnite studied from this locality falls within the area indicated by Spry (1984) for gahnite occurring in aluminous metasediments (Fig.24). In the aluminous rocks at Swartkoppies, gahnite exhibits a far greater range in Zn content than the sulphide associated gahnite at Broken Hill or gahnite in quartzites at Achab.

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Table 18. Average (or representative) analyses of biotite and gahnite fran 9.i.artkoppies.

BIOTITE

n 4 1 SJlMJLE 9< 3 9< 4

<:f Si02. 35.42 0.44 35.35 Ti02 1.53 0.37 2.41 Al203 19.72 0.22 19.78 FeO 16.ro 0.48 17.83 MnO 0.14 0.02 0.00 MgO 12.ro 0.48 10.23 \

eao nd nd ZnO nd nd Na20 0.32 0.06 0.33 K20 8.25 0.16 8.23

Total 94.58 94.20

GOJ-!NITE

n 13 12 11 2 StWLE 9< 2 9< 3 9< 4 9< 10

<S 6 rJ 6 Al203 58.28 0.45 57.76 0.28 57.64 0.54 56.32 0.02 Cr203 0.05 0.05 0.24 0.03 0.11 0.03 nd FeO 15.68 0.48 25.02 0.35 20.86 0.65 15.98 0.48 MnO 0.13 0.06 0.35 0.03 0.26 0.03 0.19 0.03 MgO 2.01 0.07 3.49 0.11 2.82 0.11 1.73 0.00 ZnO 24.31 0.38 13.24 0.28 18.40 0.34 25.02 0.96

Total 100.46 100.10 100.09 99.24

nd: elerrent was not detected or the anoont detected was belCJN the.detection 1 imit of the analytical rrethx! e!JlJioyed. 6: is a statistical rreasure of the range of 'n' nlJTber of analyses.· All Fe is analysed as FeO.

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SPIN EL

Figure 24:

GAHNITE

r---, I \

I \ I ' I \ I \ I \

~ ..), I 'V '\).

\ \1o, I I I \ I \ I \ I \

\ .. \ I \ I \ I \

\ "\ I \ I \ I \ I \

\ \ I \

\ \ I \ I \ I \ \ \ I \

HERCYNITE

Symbols: open triangjes : closed tria~gles: closed squares : dots

porphyroblastic fibrolite-gahnite massive gahnite rock fibrolite-gahnite rock sillimanite-gahnite-biotite rock

demarcated ~ield: gahnite associated with aluminous metasedimen;s (Spry, 1984).

rock

Gahnite compositions (Swartkoppies) plotted on a triangula1 endmemb~r diagram.

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The zinc-rich gahnite in the porphyroblastic fibrolite-gahnite rock has the compositional range Ghnsa-saHC3s-3aSP7-10 and in the massive gahnite rock Ghns1-ssHC3s-aoSPa-10• Zincian hercynite from the fibrolite-gahnite fibrolite rock has a compositional range of Ghn3a-a1HCaeSP13• In the recrystallised sillimanite-gahnite-biotite rock, zincian hercynite has the compositional range; Ghn27-30HCsa-saSP1a-17• Plotting gahnite compositions in terms of their cation variability indicates an inverse relationship between Fe and Zn (Fig.25), and between Mg and Zn -(Fig.26). On both diagrams compositions of gahnite in the massive gahnite and porphyroblastic gahnite-fibrolite rocks overlap to some extent and contain the highest zinc contents. A plot of the Mg/Mg+Fe vs. Zn/Zn+Fe ratio of gahnite (Fig.27) indicates little variation in Mg/Fe ratio in gahnite from Swartkoppies.

Zoning in gahnite

Minor compositional zoning occurs in colour zoned gahnite grains. In the porphyroblastic gahnite-fibrolite rock this is shown by an increase of 0.5 - 2 wt% ZnO and a similar decrease in iron content from core to rim, corresponding to the colour variation of dark green cores and pale to colourless rims. Zoning is discussed in more detail in chapter 5.3.

4.4.3 Metamorphism

The sillimanite-corundum rocks at this locali~y are hosted in a sillimanite-biotite-garnet metapelitic schist. No geothermometric estimations or calculations have been applied to Swartkoppies rocks in previous studies and unfortunately none of the metapelitic schist samples were .available for this study. Similar sillimanite-corundum rocks are, however, found in the aluminous schist at Achab and Aggeneys (Moore 1977, 1980, 1986) and the metapelitic schist at Swartkoppies is correlated with the Namies schist at Achab (Moore, 1977) and the Aluminous schist at Aggeneys (Joubert, 1970) by SACS (1980). At the two last named localities three metamorphic events have been determined (Moore 1977, SACS 1980, Ryan et al., 1982) with a maximum grade of upper amphibolite facies.

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0 c:

N

*

22

•• •

'i 16

• ,...

10 '--~~-'-~~__;1...-~~-'-~~-'-~~~L..-~~-'-~~ 14 20 26

wt% FeO

Symbols: open triangles : closed triangles: closed squares dots

porphyroblastic fibrolite-gahnite massive gahnite rock fibrolite-gahnite rock sillimanite-gahnite-biotite rock

rock

Figure 25: Gahnite compositions (Swartkoppies), Zn0/F€0.

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0 c:

N

25

20

15

10

-

...

I

0 1

I

/:;.

/:;. .. ~ 15.£::,,.

• ••

• . ·'J

I I I

2 3 4 ''

wt% MgO

Figure 26: G ah lite compositions (Swartkoppies), ZnO/MgO.

Figure 27:

QI

.... 0·5 + Cl

~ ::E

... -

...

-

.

-.. , ~

I

s~:J, 0·5

Zn/.'.: /Zn+ Fe

open t~iangles : closed triangles: closed squares dots

porphyroblastic gahnite-fibrolite massive gahnite rock gahnite-fibrolite rock gahnite-sillimanite-biotite rock

rock

Gahnit. compositions (Swartkoppies), Zn/Zn+Fe vs. Mg/Mg+FE -86-

Co-existing sillimanite-bi?tite-garnet at Swartkoppies indicates that similar metamorphic grades were attained in the area. Regional metamorphism of amphibolite to upper amphiblite grade is assumed in the Swartkoppies area with temperatures.of 650 ±50 °C and pressures of 4 - 5 kbar, based on the calculations made in chapters 4.2.3 and 4.3~3.

4.4.4 Gahnite Formation

Similar gahnite-bearing, garnet-sillimanite schists and gneisses to those at Swartkoppies, are associated with the metamorphosed massive sulphide deposit at Broken Hill, Australia (Plimer 1977, Segnit 1961). Segnit (1961) proposed that the garnet-sillimanite rocks formed as a result of metamorphism of argillaceous (kaolinite-rich) sediments and that gahnite formed, during metamorphism, from zinc absorbed onto clay minerals e.g.; Al2Si20s(OH)a + ZnO(in kaolinite)= ZnAl20a + Si02 + 2H20.

The absence of a zinc-bearing aluminous phase at Swartkoppies (sillimanite, biotite and magnetite did not contain zinc) reduce the probability of gahnite formation by breakdown of a zinc-bearing precursor mineral phase, but do not necessarily exclude it. However, the porphyroblastic and massive habit of gahnite, the similarity of the stratigraphic column with that at Achab and Aggeneys (Fig.2) and the presence of concentrations of sulphides in Bushmanland Sequence rocks at a number of localities in Namaqualand (Rozendaal 1982, Moore 1986) suggests that sphalerite might be the precursor Zn phas~ at this locality. At Aggeneys and Gamsberg small quantities of .sulphides occur in the rocks surrounding the ore body (Ryan et al. 1982, Rozendaal 1982) and there is evidence for sulphides occuring in more than one stratigraphic horizon in these ore bodies (Moore, 1986). It is proposed that, similar to the Aggeneys and Achab localities, gahnite formed during prograde metamorphism from ZnS-bearing shales. The presence of magnetite in the sillimanite-biotite-gahnite assemblage indicates oxidising conditions during metamorphism and supports the formation of gahnite and zincian hercynite by a reactions such as; 2Al 2Si 205 (0H)a -> Al2SiOs + Al203 + 3Si02 + 4H20 and 2Al2Si20s(OH)a + ZnS + 4FeS2 + 402 -> 2(Fe,Zn)Al20a +

Fe30a + 4Si02 + 4H20 + 3/252.

-8?-

The host si11imanite-corundum rock contains very little Si in the form of free qu~rtz and it is unlikely that the compositional variation (Fe, Zn) of gahnite between samples can be explained in t~rms of disequilibrium of gahnite-sillimanite. Rather, it is proposed that limited mobilization of Zn and Al species resulted in the formation of gahnite in an essentially closed-system metamorphic environment. Hence the variation of Zn and Fe . components of gahnite at this locality is largely a function of the availability of components (i.e bulk chemistry).

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4.5 ORANJEFONTEIN

At Oranjefontein, on Vioolskraalberg, gahnite occurs in small quantities in almost all lithological types overlying the quartzo-feldspathic gneiss. For the purpose of description these rocks are divided into rocks in which gahnite occurs mainly as an accessory phase; the aluminous schist, metapelitic rocks and glassy quartzites, and where blue and green gahnite occurs as major phases; the quartzites and garnet-rich rocks occuring at the interface between the aluminous schist horizon and the overlying massive quartzite unit. This locality formed part of the investigation into mineralogic anomalies in the Namaqualand Metamorphic Province supported by the CSIR as part of the National GE!oscience Programme. The Oranjefontein gahnite occurrence is described in a paper by Hicks et al. (1985) and much of the information contained therE!in results from this study and that which formed part of an unpublished honours project (Hicks, 1983).

4.5.1 Petrography

A geological map of Vioolskraalberg is shown in Figure 6 and the description of the stratigraphic succession at this locality is given in chapter 3.3.4. A petrographic description of the lithologies, as they appear in the stratigraphic column, is given below. Estimated modal proportions of minerals present in the samples studied at this locality are given in Table 19.

Quartzo-feldspathic gneiss

As these rocks are not of particular relevance to this study, they are only mentioned briefly. The biotite-rich, quartzo-feldspathic rock crops out locally as a nodular pink-weathering leucogneiss. The leucogneiss owes its distinctive pink colour to the presence of K-feldspar (>90 mol% orthoclase). Lens-shaped sillimanite segregations weather positively and give the rock a nodular appearance. Locally these rocks contain some garnet and amazonite.

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Table 19. Estimated nodal prq:iortions l minerals present in sanples st<.died at Oranjefontein.

PINK GNEISS AU If\OJS SCHIST

SJ!MlLE JE 10 JE 12 JE 3J JE 27 JE 11 JE 13 JE 28 JE 29

Quartz 75 55 75 00 00 65 85 75 00

Biotite m 10 m 10 10 m m m

Chlorite m m m

f'luscovite Hercynite tr tr tr

Mlgnetite m m m m m

Cordierite 10 3) 20 20 m m 10

Ortroclase m 10 m 15

Sillimanite 5 Garnet m m Sericite 20 3) m m m m m

Zircon tr tr tr tr tr

Goethite tr tr tr

Epicbte Hematite tr Rutile tr tr

ALLMit\OUS SCHIST IOTITE-GARNET- ~IVE ALTERED CARNET-BIOTITE ROCKS &.oRDIERITE SCHIST GARNET

ROCK

SDWLE JE 33 JE 34 JE 31 JE 32 JE 44 JE 36

Quartz 00 75 45 m 10

Biotite m m 3) fl)

Chlorite f'luscovite Green gahnite Blue gahnite m

Hercynite Mlgnetite m m Hematite m

Cordierite 25 10 m 3)

Ortllxlase m Si 11 imanite m Garnet 15 15 00

Seri cite m m

Zircon tr tr tr Goethite tr tr tr

Epicbte Rutile tr

'm' refers to minerals present in m·nor pr~rtions (5% or less) 'tr' refers to minerals present in race quantities (1% or less)

-90-

m

55

tr tr

JE 35 JE 82 JE fl)

3) 45 10

m 10 m

m 10

fl) 45 m 45

m tr

tr

Table 19. Estimated rrodal proportions of minerals present in sarrples studied at Oranjefontein.

ALTERED Gl\RNET-BIOTITE ROCKS Gl\RNET-BEARIMl

SIM>LE JE 7 JE 9 JE 16 JE 19 r-ET~ARTZITES

JE 18 JE 14 JE 15

Quartz 3) m Biotite €() 8) 90 90 Chlorite 65 m 10 m m m M.Jscovite Green gahnite 15 20 Blue gahnite 10 m m Hercynite tr Magnetite m Hematite m Cordierite Orth:x:lase Sill imanite Garnet 15 m m tr tr Seri cite 10 Zircon GJethite m m m Epicbte 15 €()

Rutile m m m m Tourmaline Galena m m

r-ET~ARTZITE

SlM>LE JE 20 JE 21 JE 17 JE 38 JE 37 JE 39

Quartz 75 95 95 95 95 95 Biotite m m Chlorite m m m M.Jscovite Hercynite tr Magnetite tr Hematite m Cordierite Orth:x:lase Sillimanite Garnet 20 tr tr Seri cite tr tr Zircon tr GJethite Epicbte Rutile tr Tourmaline m m

· Galena tr tr

'm' refers to minerals present in minor proportions (5% or less) 'tr' refers to minerals present in trace quantities (1% or less)

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Table 19. Estimated m:xlal prop:::>rtio s of minerals present in sam::>les studied at Oranjefontein.

GA.HNITE (ff'HlcmPITE, GARNET) QJARTZITES

SJ!WLE JE 1 JE 2 JE 3 JE 4 JE 6 JE 74 JE 5

Quartz 75 70 55 75 ro ro 95 Biotite ••• altered 10 10 10 10 m m m

Chlorite MJscovite Green gahnite m m 20 m m m Blue gahnite m 10 10 10 m m m Hercynite Magnetite Hematite m m m m m Garnet tr tr tr tr tr tr tr Rutile tr tr tr tr tr tr tr Seri cite tr tr tr tr tr tr tr Goethite tr tr tr tr tr tr Galena m

GOJ1NITE ( +PHL ITE,GARNET) GAHNITE QJARTZITES QJARTZITES

SllWLE JE 78 JE 51 OF 3 JE 88 JE 22

Quartz 45 65 65 00 00 Biotite m ••• altered 15 15 m

Chlorite m M.Jscovite Green gahnite m 15 10 20 20 Blue gahnite 25 10 m 25 Hercynite Magnetite Hematite 10 m 10 20 m Garnet Rutile tr tr tr Seri cite tr tr tr tr tr Goethite tr m tr tr Galena

'm' refers to minerals present in inor prc>JX>rtions (5% or less) 'tr' refers to minerals present in race quantities (1% or less)

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JE 23 JE 24

75 55

10 20 10 10

m 10

tr tr tr tr

JE 25 JE 26

00 75

10 20

10 m

tr tr

Metapelitic Schist

Cordierite-bearing metapelitic schist forms the major stratigraphic horizon between the quartzo-feldspathic gneiss and overlying quartzites. Biotite, quartz, cordierite and sillimanite form the major constituents of this rock (Table 19). Assemblages observed include; quartz+ feldspar + biotite + sillimanite (±garnet, magnetite) and quartz+ cordierite + sillimanite + biotite (±magnetite, green spinel, feldspar). The feldspar is untwinned albite (Abs4An40r2l· The majority of the matrix is composed of medium grained interlocking quartz grains. Magnesium-rich cordierite occurs interstitially, commonly with circular inclusions of quartz. Most of the cordierite is altered to pinnite. Feldspar does not occur in direct contact with cordierite, and is invariably sericitised. Quartz generally constitutes in excess of 50% of the rock, while cordierite and feldspar comprise between 15 and 30%. The remaining major constituents ~re silljmanite and biotite which are aligned within the foliation plane. Biotite is orange-brown and generally occurs as blunt laths. Alteration of biotite produces narrow, lens-shaped inclusions of quartz parallel to the biotite cleavage which is outlined by minute blebs of haematite, goethite and rutile. Garnet is present in minor quantities (< 3%). Garnet grains are euhedral, commonly fractured and less than 0.5 mm in diameter. Magnetite, containing inclusions of exsolved green hercynite, is a common, accessory phase generally associated with cordierite.

Narrow horizons of more resistant biotite-garnet-cordierite schists occur locally within the aluminous schist. Minor quantities of quartz, sillimanite and green spinel form part of the assemblage. Garnet occurs as 2.5 mm fractured grains and contains inclusions of biotite and quartz. Cordierite and biotite are coarse grained, the cordierite invariably pinitised. Biotite constitutes the most abundant phase and is pleochroic, dark brown to green-brown. Minute grains of quartz are occasionally found in association with biotite or cordierite.

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Massive Garnet and Garnet-biotite Rocks

Withiri the aluminous schist horizon, below and at the interface between the schist and the quartzite, pod-like bodies of garnet-biotite, massive garnet and garnet-biotite-gahnite rocks occur. These are restricted in extent and are preserved within the major synformal fold closure (Fig.5). In the garnet-biotite rocks, garnet constitutes 60 - 70% of the rock with up to 40% biotite and rare green gahnite. The green gahnite invariably occurs as inclusions in garnet. Garnet occurs as subhedral 0.3 to 0.5 mm grains. Blue gahnite, when present, is associated with biotite alteration. Most biotite is altered by retrograde metamorphism and replaced by chlorite and rutile in non-gahnite-bearing assemblages. Epidote-chlorite-garnet rocks within the same stratigraphic horfzon as the garnet-biotite rocks are interpreted as altered equivalents of the latter.

In gahnite-bearing, garnet-biotite rocks biotite is replaced by quartz, sericite, oxides and blue gahnite (Fig.28a). The .alteration products mimic the biotite grain shape with minute blebs of hematite, goethite and rutile outli~ing the grain border and cleavage traces and blue gahnite infilling the spaces between the traces. In massive garnet rocks, blue gahnite may comprise a substantial proportion of the assemblage. It occurs as narrow rims around garnet grains or infills fractures in garnet (Fig.28b}. In these rocks fractured garnet grains are eroded and possibly act as a nucleation site for blue gahnite. Green gahnite occurs as rare inclusions in garnet in the massive garnet rocks and is invariably surrounded by blue gahnite.

Locally an outcrop of garnet-bi~tite-gahnite-quartz rock contains 10 - 20 % green gahnite. Gree~ gahnite and garnet occur as coexisting porphyroblastic phases with interstitial altered biotite and fine grained, recrystallised quartz (Fig.28c). Blue gahnite, if present, is associated with altered biotite and quartz (Plate 5). Where blue gahnite is not present, quartz appears to form part of a retrograde chlorite-quartz assemblage. It appears that these rocks, like the epidote chlorite rocks (above), are the altered equivalents of garnet~biotite rocks.

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0·3mm 1-...---1

a. Garnet-biotite rock. b. Massive garnet rock.

The matrix is composed m stly of hematite. Blue gahnite, uartz and hematite replace biotite. Hematite infills fractures in garnet:

Blue gahnite surrounds garnet grain The matrix is composed mostly of hematite.

Tmm L.___J

c. Garnet-biotite-gahnite-quartz rock.

Blu. gahnite, biotite and garnet ~ur~ound green gah~ite. Hemati~e . 1nf1lls fractures 1n garnet. B1ot1te is ~eplaced by hematite and blue . gah1ite and appears as elogate, ellJpsoid shapes, defined by the c 1 ec:tvage traces.

Abbreviations: B - biotite, Bg - blue gahnite, Ga - garnet, Gg - green gahnite, H - hematite, Q l quartz.

Figure 28: Textures in the garnet-rich lithologies at Oranjefontein.

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r

A distinctive green coloured, galena-bearing rock occurs in the upper layers of the aluminous schist on the south facing side of Vioolskraalberg. Epidote, sericite, chlorite and galena form the major constituents with disseminated galena making up approximately 5% of the rock. Occasional grains of magnetite, green spinel and rare, highly corroded garnet grains occur as minor constituents. The texture of this rock suggests complete replacement of a precurser garnet-biotite assemblage similar to the piemontite-chlorite rocks which occur at the same horizon on the western limits of the syncline. The different mineralogies of the altered garnet-biotite rocks are explained in terms of retrograde metamorphism of garnet-rich rocks with slightly different bulk chemistries.

Summary Textural evidence indicates the presence of both a prograde and retrograde assemblage in the garnet-biotite and massive garnet rocks. Green spinel, garnet, and biotite are assoc'iated with the prograde assemblage whereas blue gahnite, quartz and i·ron oxides are associated with biotite alteration as a retrograde assemblage. In non-gahnite-bearing assemblages epidote and chlorite replace garnet-biotite assemblages or chlorite replaces biotite.

In the massive garnet rocks, garnet is corroded and infilled by blue gahnite. In the gahnite-rich garnet-biotite-quartz rocks, quartz occurs as a late stage mineral phase associated with retrograde minerals such as chlorite or blue gahnite. Green gahnite appears to be out of equilibrium with the assemblage and is rimmed by garnet, altered biotite or blue gahnite. Blue gahnite is associated with altered biotite which appears to be replaced by blue gahnite, iron oxides and quartz.

Green spinel is generally rare in the massive garnet rocks, but where it occurs is always associated with the prograde garnet-biotite assemblage.

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Gahnite-bearing Quartzites

These rocks generally contain 10% or more gahnite and crop out between the aluminous schist and massive quartzites on the southern and western sides of Vioolskraalberg. Although they occur in a stratigraphically equivalent horizon to the massive garnet and garnet-biotite rocks, they have far greater lateral extent (Fig.6). On the western flank of Vioolskraalberg the assemblage is quartz + blue gahnite + green gahnite + phlogopite (+ rutile, garnet, galena). To the south, the gahnite quartzites contain a higher proportion of gahnite and no garnet or mica. Texturally the rocks to the west display evidence of a precursor pelitic component in the assemblage whereas this is either absent or masked by retrograde overprinting in the gahnite quartzites on the southern flank of the Vioolskraalberg.

Gahnite (+ phlogopite, garnet) quartzites

The matrix of these rocks is composed of coarse grained, interlocking quartz grains. Anhedral, green gahnite grains comprise 5 - 7% of the rock, have an average grain size of 0.5 mm and commonly are embayed to quartz. Blue gahnite comprises up to 10% of the assemblage and forms <0.1 mm grains which are dispersed throughout the matrix and also occur in aggregates. Altered phlogopite and tiny garnet grains occur throughout these rocks (Plate 6). Blue gahnite also commonly occurs as rim to green gahnite porphyroblasts (Plate 7). Haloes composed of tiny blebs of iron oxides surround blue gahnite aggregates and are believed to be the remains of altered phlogopite (Plate 8). The phlogopite "ghosts" are recognised as concentrations of fine hematite along original grain boundaries and cleavage traces whereas blue gahnite and quartz crosscut the former grain boundaries (Plate 6). Rounded grains of rutile and tiny garnet grains occur in minor to trace ~uantities throughout the matrix of these rocks. Rare unaltered phlogopite grains occur as inclusions in quartz but most phlogopite appears to have been replaced by quartz, iron oxides, rutile and blue gahnite. One sample contained approximately 5% galena in the form of coarse (-lomm) crystals and as fine grained, disseminate inclusions in quartz. The galena is partially replaced by anglesite.

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Gahnite Quartzites

In these rocks coarse, crystalline green gahnite occurs as poikiloblastic porphyroblasts w1th abundant, fine-grained quartz inclusions. Blue g~hnite comprises more than 20% of the rock and generally forms large aggregates made up of small (-0.1 mm), euhedral grains. The matrix of these rocks is composed of fine grained recrystallised quartz, commonly exhibiting a mortar texture. Webbed masses of hematite needles comprise up to 10% of some rocks and are associated with aggregates of blue gahnite. The characteristic biotite outlines and rutile found in the west facing rocks are absent and instead, extremely fine-grained iron oxides define elongate, wavey, lens-shaped outlines (Plate 7). These may represent the last traces of a coarse-grained precusor phase such as occurs in the garnet-biotite rocks but the effects of retrograde metamorphism mask most of the confirming evidence for this. An unusual feature in some ro'Cks is the presence of euhedral blue gahnite grains containing a central, circular portion defined by a rim of very fine-grained, red coloured, hematite (Plate 9).

Summary Green and blue gahnite are major mineral phases in these rocks. Green gahnite is coarser grained, commonly porphyroblastic and surrounded by a narrow rim of blue gahnite. Blue gahnite is finer grained and commonly occurs as aggregates composed of euhedral (-0.1 mm) grains or as rims to green gahnite. Hematite and blue gahnite are associated with r~trograde replacement of biotite and green gahnite. Retrograde alteration of phlogopite results in in situ replacement by quartz, blue gahnite, iron oxides and rutile. The retrograde overprint is more pervasive on the

I

southern limits of the syncline where green gahnite is ubiquitously rimmed by blue gahnite and traces of any precursor assemblage has all but disappeared. On the western limits of the syncline, green gahnite contains quartz inclusions and appears to be stable with respect to quartz.

\.

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Massive Glassy Quartzites

White, glassy, coarse-grained, metaquartzites overly· the metapelitic schist, forming a prominent capping to Vioolskraalberg. These contain local concentrations of tourmaline, biotite, Fe and Fe-Ti opaques and garnet. Towards the base of the quartzite unit in the south, concentrations of garnet comprise up to 20% of the rock. Blue gahnite occurs in cracks and fissures in the lower horizons of the quartzite. In a few instances a central core of green gahnite is surrounded by a radiating corona of blue gahnite which occupies fissures in the rock and forms a network of veins up to 30 cm from the green gahnite core.

4.5.2 Mineral Chemistry

Bulk rock analyses of a gahnite quartzite and gahnite-bearing, garnet-biotite rock are liste~ in Table 20 (analyses by courtesy of Dr. J.M. Moore). Trace quantities of galena and chalcopyrite were observed toward the base of the metaquartzite unit and minor proportions of galena occur locally in the underlying gahnite quartzites and an epidote-chlorite rock. Thus the presence of up to 5000 ppm Pb and trace quantities of Cu in the whole rock analyses are taken to indicate the presence of minor sulphides, now oxidised. Table 21 lists average analyses of the minerals in the samples.

Garnet

' Average endmember garnet compositions in the assemblages studied are listed in Appendix 3 and are plotted on an endmember diagram, Figure 29.

Garnet composition and habit vary considerably throughout the stratigraphic column at Vioolskraalberg. The variation probably reflects differences in bulk rock chemistry and varying degrees of the retrograde metamorphic overprint.

Almost all garnets are of the Fe-Mg-Mn series. Garnet in the quartzo-feldspathic gneiss is the one exception with an endmember composition of Alm37$pessaaPY12Gross11• In the metapelitic garnet-

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Table 20. ~le rock analyses of t gahnite-bearing rocks fran Oranjefontein.

SarrlJle: OF-7 F-8

Si02 95.71 38.13 Ti02 0.04 1.01

, Al203 1.21 22.07 FeO 1.33 16.68 ml 0.15 4.20 M:P 0.47 5,95 eao 0.03 0.81 Na20 0.04 0.18 K20 0.00 0.04 P205 o.oo 0.3) H20t 0.57 3.44 H20- 0.11 0.29

Total 99.55 92.81

Trace elerrents (ppn . Rb <2 (3

Ba 8.3 297 Sr <2 7 Th 21 91 u <3 <5

·Zr 36 559 Nb . <1 18 ~ <1 6 Sc 1 14 Ni 1.7 6.6 Pb 4270 6165 Zn 13:>5 4.19% Cu 52 78 y 4 44 La <2 81 Ce 6.8 154 Nd <3 69

Rock Types: OF-7: Gahnite(+p1 logopite,garnet) quartzite OF-8: Garnet-bio ite-gahnite rock

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Table 21. Average (or representative) analyses of minerals fran s~les studied at Oranjefontein.

~ET

n 4 6 2 4 3 2 Sl!WLE JE 2 JE 3 JE 7 JE 10 I JE 14 JE 19

cf <f rf rf a- <J Si02 39.22 0.19 38.64 0.26 37.56 0.26 36.86 0.20 37.23 0.09 38.11 0.51 Ti02 nd 0.04 0.00 nd 0.07 0.02 0.14 0.01 0.05 0.01 Al203 22.00 0.05 22.04 0.23 21.00 0.20 21.41 0.14 21.03 0.19 22.15 0.11 FeO 18.41 0.67 18.85 0.93 20.05 0.00 17.11 0.22 8.59 0.13 15.49 0.10 r.\'10 9.59 0.11 10.10 0.52 13.84 0.41 18.00 0.10 22.94 0.28 12.35 o.ro fv4gO 9.11 0.34 8.42 0.00 5.07 0.73 3.05 0.10 4.00 0.13 8.92 0.42 CaO 2.12 0.04 2.27 0.22 l.93 0.06 3.76 0.04 4.98 0.01 2.23 0.04 Na20 nd nd nd nd nd nd K20 nd nd nd , nd nd nd

Total 100.53 100.36 99.53 101.06 98.99 99.3)

~ET

n 4 3 3 3 3 7 Sl!WLE JE 20 JE 29 JE 31 JE 32 JE 35 JE 36

Cf 0 <f cf <f d Si02 38.00 0.10 37.73 0.16 37.41 0.46 37 .31 0.58 38.36 0.23 37.39 0.26 Ti02 0.06 0.01 nd nd nd nd 0.07 0.02 Al203 22.00 o.oo 22.28 0.20 21.79 0.3) 22.02 0.23 21.87 0.18 20.86 0.37 FeO 12.68 0.11 28.02 0.33 29.85 0.77 3).34 O.Ei6 14.47 0.04 18.09 0.36 t-\10 15.9) 0.20 2.26 0.02 3.18 0.27 4.00 0.40 14.77 0.79 17.29 0.17 fv4gO 8.91 0.04 8.38 0.43 6.22 0.84 5.86 0.70 7.79 O.Ei6 3.54 0.20 CaO -2.13 0.03 1.62 0.04 1.61 0.02 0.64 0.05 2.69 0.15/ 2.34 0.04 Na20 nd nd. nd nd nd nd K20 nd nd nd nd nd nd

Total 100.18 100.29 100.06 100.97 99.95 99.58

nd: element was not detected or the arrount detected is belo,.,i the detection limit of the analytical irethod ~loyed. o: is a statistical measure of the range of 'n' m.rrber of analyses. All Fe is analysed as FeO.

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Table 21. Average (or representati 'e) analyses of minerals fran Sar!1Jles studied at Oranjefontein.

Gn.RNEf

n 2 1 2 2 Sl!WLE JE 18 JE 74 JE 82 OF 7

r:f (f <f Si02 39.00 0.13 38.C6 37.99 0.07 37.69 0.17 Ti02 nd nd nd 0.00 0.01 Al203 22.78 0.01 21.70 21.62 0.01 21.98 0.16 FeO 15.96 0.01 15.70 16.78 0.29 18.37 0.52 t-tiO 10.85 0.01 14.04 11.62 0.12 9.52 0.72

~ 9.74 0.00 8.56 9.15 0.11 9.C6 0.79 CaO 2.17 0.01 1.58 '1.69 0.16 2.10 0.09 Na20 nd nd nd nd K20 nd nd nd nd

Total 100.56 99.63 98.85 98.77

CORDIERITE Pl..PGIOCLASE ORTl«L.ASE

n 4 3 1 2 1 Sol'IPLE JE 29 JE G JE 29 JE 10 JE 10

(f <f cf Si02 48.83 0.17 f:JJ.97 o. 66.23 66.56 0.23 62.00 Ti02 nd nd nd nd 0.04 Al203 33.72 0.35 34.20 20.31 19.84 0.35 18.72 FeO 5.59 0.22 2.45 0.11 nd nd t-tiO 0.20 0.02 nd nd nd nd ~ 10.15 0.32 12.22 nd nd nd CaO nd nd 0.63 0.31 0.11 nd Na20 0.09 0.02 0.15 o. 7.55 11.20 0.00 0.91 K20 nd nd 0.11 O.C6 0.02 14.41

Total 98.58 99.99 94.94 97.97 96.88

nd: e 1 errent was not detected or t arrount detected is belOIJ the detection ;limit of the analytical rrethod erJ1)1 ~d. cf: is a statistical rreasure of th range of 'n' nl.ll'ber of analyses. All Fe is analysed as FeO.

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Symbols: dots circles

closed triangles: open triangles : closed squares open squares

SPESSARTINE

GROSSULAR

gahnite(+phlogopite, garnet) quartzites gahnite-biotite-gahnite-quartz rocks and garnet-biotite rocks garnet-, gahnite-bearing metaquartzite garnet-bearing metaquartzite metapelitic schists garnet-biotite rocks

Figure 29: Garnet compositions from Oranjefontein plotted on a triangular

endmember diagram. -103-

Table 21. Average (or representativ ) analyses of minerals fran sarr1)les studied at Oranjefontein.

BIOTITE

n· 6 6 3 3 2 SoiVPLE . JE 2 JE 29 JE 31 JE 32 JE74

<1 <1 cf cf <1 Si02 37.40 1.71 35.54 0.56 3µ.61 0.26 35.99 0.35 38.24 0.04 Ti02 4.82 0.68 3.31 1.07 3.14 0.12 3.25 0.00 0.74 0.35 Al203 16.a:i 0.32 17~72 0.56 16.52 0.13 16.19 0.19 16.15 0.91 FeO 9.89 0.59 13.63 2.00 12.28 0.79 13.45 0.47 5.81 0.83 M'lO 0.25 0.03 0.13 o.a:; nd nd 0.22 0.13 fig() 17.69 0.67 14.8:> 2.03 15.86 0.8) ·15.59 ·0.19 21.X> 0.26 CaO nd nd nd nd nd ZnO 0.35 0.07 nd nd nd 0.34 0.25 Na20 0.22 o.a:; 0.10 O.C6 0.21 0.03 0.23 0.02 0.35 0.01 K20 8.95 1.19 9.33 0.21 9.41 0.18 9.26 0.17 8.f:O 0.12

Total 95.62 94.26 94.03 93.96 91.75

nd: el eirent was not detected or the arrount detected is belON the detection limit of the analytical rrethJd errployed. 6: is a statistical rreasure of the range of 'n' nllli:>er of analyses. All Fe is analysed as FeO.

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Table 21. Average (or representative) analyses of minerals frc:rn sarrples studied at Oranjefontein.

CHLORITE

n 5 4 3 7 5 SIM'LE JE 7 JE 14 JE 16 JE 18 JE 19

d cf 6 d d

Si02 31.32 1.24 24.05 0.73 27.17 1.39 27.09 1.67 27.06 1.89 Ti02 nd nd nd 0.18 0.10 nd Al203 21.10 0.40 21.71 0.55 19.55 0.54 20.09 0.92 21.68 0.83 FeO 7.04 1.28 26.86 0.93 19.98 0.19 18.34 1.26 23.68 1.57 r.tlO 1.62 0.13 2.05 0.20 2.21 0.10 2.11 0.12 1.71 0.22

M:P. 24.52 1.24 11.00 0.97 18.32 0.10 15.69 1.28 11.73 0.37 CaO 0.06 0.01 nd nd nd 0.13 0.04 ZnO 0.81 0.06 1.95 1.19 1.51 0.12 3.42 0.95 2.12 0.49 Na20 nd nd nd 0.04 0.02 0.00 0.04 K20 0.00 0.03 nd nd 0.03 0.02 0.13 0.05

Total 86.55 87.70 88.74 86.99 88.32

CHLORITE

n 11 5 S!M'LE JE 36 OF 7

d <f Si02 27.41 0.25 24.96 1.04 Ti02 nd nd Al203 19.25 0.21 ,20.66 1.32 FeO 10.19 0.84 24.31 2.74 r-tiO 3.35 0.34 1.67 0.15 M:P 21.95 0.22 13.25 1.88 eao 0.04 0.03 0.04 0.02 ZnO 5.04 0.52 1.05 0.29 Na20 0.04 0.02 nd K20 nd nd

Total 87.27 85.94

nd: eleirent was not detected or the arrount detected is belON the detection limit of the analytical 11Etroo errployed. 6: is a statistical 11Easure of the range of 'n' nurrber of analyses. All Fe is analysed as FeO.

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3 JE 20

cf 25.86 0.19 nd

20.58 0.47 21.63 0.21 2.49 0.00

14.82 0.20 0.05 0.01 2.00 0.05 0.03 0.01 nd

88.06

Table 21. Average (or representativ.) analyses of minerals fran s~les studied at Oranjefontein.

PWHIBOLE PYROXENE

n 2 1 3 2 SPM>LE JE A JE G JE A JE G

<f if rf Si02 41.49 0.62 42.39 52.36 0.52 !:().39 0.27 Ti02 1.52 0.18 0.53 0.12 0.02 0.00 0.01 Al203 15.75 0.23 19.02 5.59 0.33 7.99 0.64 FeO 9.55 0.()) 14.59 15.15 0.10 17.85 0.33 MnO 0.72 0.02 0.17 1.61 0.00 0.16 0.01 Mi> 14.00 0.33 18.49 26.38 0.47 24.87 0.37 eao 11.22 0.00 0.62 b.24 0.03 0.10 0.03 Na20 2.16 0.01 2.00 nd nd K20 0.64 o.a; nd nd nd

Total 97.85 97.89 101.45 101.45

All Fe is analysed as FeO.

REPRESENTATIVE ANALYSES OF EPICX>TE

n 4 5 SPM>LE JE 16 JE 7

rf 6 Si02 37.94 1.00 35.97 2.00 Ti02 nd nd Al203 ' 25.18 0.70 22.47 2.25 Fe203 12.23 0.76 8.96 3.25 MnO 0.77 0.45 5.11 4.31 Mi> nd 0.15 0.13 CaO 22.79 0.65 21.95 1.46 Na20 nd nd K20 nd nd

Total 98.91 94.61

Fe was analysed as FeO and has been ~calculated to Fe203. ·

nd: eleirent was not detected or the arroont detected is belo.v the detection 1 imit of the analytical irethod 6'J1)10J d. rf: is a statistical measure of the range of 'n' nl.llber of analyses.

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Table 21. Average (or representative) analyses of minerals fran saJl1'.)l~s studied at Oranjefontein.

'

C?JlaJITE

n 5 4 1 2 10 3 SlM'LE JE 2 JE 2 JE 3 JE 3 JE 15 JE 14

I

COLOJR blue green blue green blue blue cf cf d cf <f <:f

Al203 55.32 0.27 58.32 0.38 55.05 0.12 58.22 o.oi 55.18 0.57 56.32 0.33

Cr203 nd 0.24 0.04 nd 0.13 0.02 nd nd

FeO 2.00 0.12 7.01 0.38 2.27 0.04 8.00 0.43 1.83 0.16 1.24 0.14

tw\'10 nd 0.19 0.04 0.05 0.01 0.20 0.02 nd nd

t-4g() 0.00 0.01 4.92 0.00 0.11 0.03 5.64 0.04 o.oo 0.00 0.07 0.04

ZnO 41.99 0.35 28.72 1.37 42.67 0.45 27.75 0.19 43.31 0.93 41.25 0.38

Total 99.47 99.40 100.15 100.54 100.41 98.88

GPH'JITE

Nr.anal. 6 2 9 4 8 1

SlM'LE JE 18 JE 18 JE 19 JE 23 JE 23 JE 26

COLOJR blue green green blue green blue <:f cf rf <:f cf

Al203 55.38 0.19 58.58 0.01 58.61 0.61 56.33 0.52 00.44 0.25 55.39 .

Cr203 nd nd 0.00 0.05 nd nd nd

FeO 2.38 0.29 8.74 0.11 8.01 0.64 1.22 0.34 4.98 0.20 1.68 Mt) nd 0.45 0.04 0.40 0.10 0.00 0.05 0.31 0.04 0.04

t-4g() 0.13 o.a; 6.02 0.01 7.01 0.16 0.14 o.oo 7.65 0.16 0.00

ZnO 41.99 0.25 27.02 0.03 25.!:i> 0.00 41.91 0.56 26.69 0.31 43.31

Total 99.88 100.81 99.61 99.68 100.07 100.50

nd: eletrent was not detected or the arrount detected is belON the detection limit of the analytical iretroo errµloyed. c(: is a statistical ireasure of the range of 'n' nl.ITber of analyses. All Fe is analysed as FeO.

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Table 21. Average (or representative) analyses of minerals fran 5alllJles studied at Oranjefontein.

GAJ-INITE

n 3 1 4 2 3 1

SoWLE JE 35 JE 39 JE 74 JE 74 JE 82 JE 82

COLOOR blue blue blue green blue green

0 cf cf <f 0

Al203 55.12 0.20 54.32 56.31 0.26 59.45 0.38 53.41 0.32 59.22

Cr203 0.07 0.04 nd nd nd nd nd

FeO 2.19 0.32 2.02 1.37 0.54 7.62 0.37 3.63 O.JJ 7 .11

f'lrl() 0.20 0.09 0.00 0.10 0.00 0.35 0.00 0.10 0.02 0.27

M:10 0.12 0.01 0.13 0.11 0.01 5.91 0.42 0.14 0.03 6.00

ZrfJ 42.26 0.12 42.16 42.75 0.61 27.32 0.81 41.13 0.38 26.99

Total 99.96 98.71 100.64 100.65 98.41 99.59

G.Lff.JITE Zlt'-CIPN HERC ITE

n 3 2 1 5 4

SDWLE OF 7 JE 16 JE 29 JE A JE G COLOOR green

0 <f (f <f <f

Al203 58.JJ 0.16 00.45 0.23 54.68 61.55 0.68 61.21 0.16

Cr203 nd nd 0.67 0.00 0.04 0.93 0.46

FeO 10.01 . 1.16 12.58 1.82 27 .37 21.62 0.79 21.63 1.79

M10 0.49 0.10 1.22 0.181 0.39 0.83 0.06 nd

~ 5.86 0.76 12.75 0.54 6.23 14.72 0.39 13.76 0.59

ZrfJ 24.73 2.20 12.79 2.42 8.31 0.48 0.24 0.3) 0.52

Total 99.39 99.79 97.65 99.29 97.83

nd: elerrent was not detected or the anount detected is belON the detection 1 i mi t of the ana 1ytica1 rretrod errp 1 dred. · o: is a statistical rreasure of the range of 'n' nlJTber of analyses. All Fe is analysed as FeO.

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biotite-cordierite schists garnet has the composition Almse-eeSpesss-11PY21-31Gross1.s-4 and is relatively almandine-rich compared to garnet occuring over the rest of Vioolskraalberg. In the massive garnet and garnet-biotite rocks, garnet is spessartine-rich i.e. Alm30-40Spess23-3ePY14-37Gross3.s-7• Garnet in the altered piemontite-chlorite rock is also relatively spessartine-rich and has an average composition of Alm44Spess31PY20Gross4.

Garnet in the metaquartzite has an average composition of Alm27SpesS33Py34Grosse. In a garnet-bearing metaquartzite, where garnet is partially replaced by chlorite and blue gahnite, garnet has a compositional range of Alm1e-22Spesss1-ssPY1s-1eGrosse-13

Variation of garnet composition with metamorphic grade is a fairly well established phenomena. With increasing metamorphic grade Fe and ultimately Mg contents increase whereas 'Ca and Mn contents decrease (Miyashiro 1973, Winkler 1967). This probably accounts for some of. the variation observed. However the alteration of biotite-garnet assemblages to garnet-gahnite-quartz- hematite assemblages in some cases and in other cases to epidote-chlorite or piemontite-garnet-chlorite must also necessarily affect the composition of the garnet. It is apparent that small scale variation in bulk rock chemistry has produced a wide array of mineral assemblages which may be the main factor in the compositional variation observed in minerals such as spinel, garnet and epidote at this locality.

Fe - Ti Oxides

Abundant hematite and goethite associated with blue gahnite are an observed feature of the gahnite quartzites. Hematite occurs as haloes surrounding small aggregates of blue gahnite in some rocks atid as webbed masses composed of tiny needles in other rocks. Hematite + goethite + rutile partially replace biotite throughout the gahnite-bearing lithologies. Ilmenite, magnetite and titanomaghemite occur as coarse blebs in the aluminous schist, generally in association with cordierite or sillimanite. Local concentrations of ilmenite and magnetite occur in the massive qu~rtzite unit. Magnetite occurs in association with green gahnite in some of the gahnite quartzites.

;-109-

'

Micas

The composition of biotite in the aluminous schist is annite with 4.5 wt% Ti02• In the metapelitic garnet-biotite-cordierite schist the mica is phlogopite with 3.5 wt% Ti02• Although biotite is a common constituent of all rock types in the study area, the pervasive affects of retrograde metamorphism have resulted in its replacement by chlorite or hematite, goethite, rutile, blue gahnite and quartz. In the gahnite quartzites, biotite armoured by quartz contained up to 0.4wt% ZnO (detection limit is 0.02 wt% ZnO). Prograde biotite from the Broken Hill massive sulphide deposit, Australia contained up to 5350 ppm zinc (Plimer, 1977). Frost (1973) found up to 0.5 wt% ZnO in biotite associated with sulphides. Zinc-bearing biotites containing 0.24 wt% ZnO are believed to be the precursor mineral to gahnite formed during retrograde metamorphism {Dietvorst, 1980).

Chlorite occurs in the garnet-biotite rocks as a replacement of biotite and in the quartzites, ·associated with blue gahnite as a partial replacement of garnet. In terms of Hey's {1954) classification (Fig.30) Oranjefontein chlorites are ripidolites and pycnochlorites. High manganese (2.8 - 4.4 wt% MnO) and zinc {0.8 - 5.4 wt% ZnO) contents are associated with blue gahnite-bearing assemblages. Similar Zn-,Mn-rich chlorites, containing up to 10 wt% ZnO and a similar quantity of MnO are associated with low temperature, hydrothermal veins at Franklin, New Jersey by Frondel and Ito (1975). They suggest that Fe and Mg can be more or less completely replaced by other divalent ions including Mn, Co, Ni and Zn.

Epidote

In the galena-bearing, epidote-chlorite rock epidote is pleochroic pale yellow-green to colourless and has the structural formula Ca1.sFeo.7Mno.osAlo.2Al20(0H)[Si207][Si04]. The endmember composition is clinozoisite (75 - 78 mol%), epidote (22 - 25 mol%) and piemontite (1 - 3 mo1%), (Fig.31).

In a maroon coloured, garnet-piemontite-chlorite rock associated with the massive garnet rocks, piemontite has a wide range of compositon (Fig.31).

-110-

.Figure 30:

Figure 31:

Cl :E + ..

0 .. i ..

QI u..

0·8 > Cl)

c: :I

QI .. 0·5 ..

2 .::. u 0 c: u ;., c.

0·2

0 ~4~~~---1-5~~~5.-5~--'-6.-2~~-'-7~~~~8

Si -

Chlorite c mpositions plotted as a function of Si and Fe

content (a ter Hey, 1954).

Clinozoisite

,,.

( . I I I \ I

' ' ' 50 moll% 50 mo/% Piemol1tite Epidote

Epidote jlotted on a triangular endmember diagram (after Ashley

1984). 1he staggered line outlines the field of natural

piemonti1

1

1e.s (from Keskinen and Liou, 1979).

-111-

The structural formula is: Ca1.eFeo.a9-o.24Mno.as-o.oaMgo-o.03Alo.2-o.02Al20H[Si204][Si04]. Garnet in this assemblage is similarly Mn-rich (17 wt% MnO) and chlorite contains 1.5 - 1.75 wt% MnO.

A massive epidote rock containing only minor quantities of quartz and chlorite was found on the western face of Vioolskraalberg at a similar stratigraphic level to the garnet-piemontite-chlorite rock. However, epidote in this rock is greenish yellow to colourless and exhibits the distinctive high interference colours of epidote (clinozoisite has low interference colours). The absence of any pink colouration indicates negligable manganese (Deer et al., 1080). It appears thus that the manganese rich lithology is limited in extent within this stratigraphic

horizon.

According to Deer et al. (1980), piemontite occurs in rocks of the greenschist facies. In general, higher oxygen fugacity conditions are required for the formation of Mn3• than Fe3•, and the presence of both (Mn3• in piemontite and Fe3• in hematite) in association with retrograde assemblages implies high oxygen fugacity conditions during the rerograde metamorphic event.

Gahnite, Zincian Spinel, and Hercynite

Several varieties of green-coloured spinel with widely differing compositions are associated with different assemblages at Vioolskraalberg. Analysed spinels are plotted on a triangular endmember diagram (Fig.32). Figures 33, 34 and 35 show gahnite compositions in terms of cation content on two axis diagrams.

Green gahnite in the gahnite(+ phlogopite, garnet) quartzites has an average composition of Ghna4SP2sHC1a and in the gahnite quartzites, where the effects of retrograde metamorphism are more pervasive, Ghns7Sp32HC11• In the garnet-biotite-gahnite-quartz rocks, green gahnite has the composition Ghns9SP2aHC1s• In gahnite-rich garnet-biotite-quartz rocks gahnite has the composition

GhnssSP30HC1s•

I

-112-

I J

...:

SPIN EL

MARBLES

----

Symbols: small dots : closed triangles: open circles : large dots closed squares open squares open triangles

GAHNITE

PEGMATITES

SULPHIDE DEPOSITS

I I I

blue gahnite

• ALUM I NOUS

METASEDIMENTS.

\ \

' ' \ HERCYNITE

gahnite(+phlogopite, garnetj tjuartzites garnet-biotite rocks gahnite quartzites aluminous schist calc ~ilicate (altered garnet-biotite rock) amphibolite and granulite rocks

Demarcated fields refer to gahnite associated with particular lithologies (from Spry, 1984).

Figure 32: Gahnite composition from Oranjefontein plotted on a triangular

endmember diagram.

-113-

30

20

0 s::

N

~ ~

~

10

. •

.._

....

...

'-

._

0

• t

• 1~4'~··

oO

I I 5

Symbols: small dots : closed triangles: open circles : large dots open triangles

10

wt% MgO

15

blue gahnite gahnite(+phlogopite, garnet) quartzites garnet-biotite rocks gahnite quartzites amphibolite and granulite rocks

Figure 33: Gahni~e compositions (Oranjefonteiri), ZriO/MgO.'

-114-

0 c: N

~ +-'

~

40

30

20

10

. . .

. -~· .. : , .. •• • •• •

••• • • •• cSO. 0 A

.~

0

Symbols: small dots : closed triangles: open circles : large dots open triangles

10 20 30 wt% FeO

blue gahnite gahnite(+phlogopite, garnet) quartzites garnet-biotite rocks gahnite quartzites amphibolite and granulite rocks

Figure 34: Gahnite compositions _(Oranjefontein), ZnO/FeO. ·

-115-

' '

I

' 1 I . I I I

._

j

I .

.. ~ fl . Q) .....

~~ + C) 0·5

. ~

~ . ::!::

... ' .

' ... I • . .. - '-i: ..

0 o.s 1

ZYz Zn+ Fe

Symbols: small dots : blue gahnite closed triangl ~.s : gahnite(+phlogopite, garnet) quartzites open squares : garnet-biotite rocks large dots : gahnite quartzites , open triangles : amphibolite and granulite rocks

-

I

Figure 35: Gahnite com~ositions (Oranjefontein), Mg/Mg+Fe vs. Zn/Zn+Fe. '

. -116-

Green gahnite occurring as a minor phase in the epidote-chlorite rocks has a compositional range of Ghnso-soSP22-29HC20 in the piedmontite rock and Ghn23-31SPs3-s7HC1s-19 in the galena-bearing, clinozoisite-chlorite rock. In both assemblages, green gahnite is ~urrounded by chlorite. Bright green zincian hercynite occurs as exsolved grains in magnetite in the aluminous schist. This spinel has an average composition of Ghn32SP2sHC42•

'

According to Spry's (1984) research, gahnite with high Mg contents are generally associated with marbles (Fig.40). However, gahnite with similar Zn contents to that occurring at Oranjefontein are reported from cordierite-anthophyllite rocks associated with mineralization at Montauben-Les-Mines, Quebec i.e. Ghnsa-ssHC1a-21SP1s-21 (Bernier et al., 1984) and at Falun, Sweden i.e. Ghnso-70HC1s-soSPo-24 (Wolter

and Siefert, 1984).

On the neighbouring farm, on the northern flftnks of Vioolskraalberg, at a similar horizon, quartz-cordierite-two pyroxene granulites contain coarse intergrowths of magnetite and pleonaste (Fe-Mg spinel ). The range of composition in these spinels is Ghn1-sSPso-soHC3s-47 and it is interesting to observe that even in these rocks spinel contains detectable quantities of zinc (0.5 - 2.3 wt% ZnO). Cordierite-anthophyllite or cordierite-orthopyroxene assemblages are frequently reported as containing small proportions of spinel. Where these rocks are associated with mineralization the spinels commonly contain a component of zinc. Similar zinc-bearing pleonastes as are found at Oranjefontein are reported by Treloar et al. (1981), Teale (1980), Schreurs and Westra (1985) and Coolen

(1981).

The blue gahnite on Vioolskraalberg is close to endmember gahnite and compared to green gahnite, shows a relatively small range in compositon i.e. Ghn9i-9aSPo-3HC1-7• Almost endmember gahnite is rare and generally occurs in low temperature, quartz-bearing rocks and pegmatites (Spry, 1984). Kramm (1977) records gahnite with composition, Ghn88Sp10Gal2 in low grade viridine-braunite-muscovite schists from Belgium and gem quality, blue spinel (GhnaaHC10SP1Gal1l associated with mineralized pegmatites in Nigeria are reported by Batchelor and

-117-

'

Kinnaird (1984). In the rocks studied here, blue gahnite is associated with a late-stage, retrograde metamorphic event and is commonly associated with quartz. Reported occurrences of blue coloured gahnite are like-wise rare, the only documentation of these found, being those of Batchelor and Kinnaird (above) and the gem quality, Mg-Zn spinels from Sri Lanka (Anderson et al. 1937, Schmetzer and Bank 1985). Batchelor and Kinnaird ascribe the blue colour to the absence of ferric (Fe3 +), which commonly substitutes for Al, in the spinel structure.

4.5.3 Zoning in gahnite

Green gahnite porphyroblasts surrounded by rims of polycrystalline blue gahnite provide a striking colour d~fference in these rocks (cover plate). The colour change is abrupt and is matched by an equally abrupt change in composition (Fig.36). Individually the two spinels are, -however, compositionally homogenous and cannot be considered as a single zoned mineral. If the blue gahnite is derived from green gahnite breakdown during a distinct, low temperature, retrograde metamorphic event, there is very little evidence for re-equilibration between the two spinel phases. The high zinc content of blue gahnite is in part explained in terms of zinc introduc~d into the rocks during retrograde metamorphism. It appears that the kinetics of new mineral growth combined with the disequilibrium of green gahnite-quartz, resulted in the formation

of the blue gahnite overgrowths.

4.5.4 Metamorphism and f (0)2

In central Namaqualand, to the south of Oranjefontein, metapelitic rocks are dominated by granulite-facies assemblages. A commonly observed assemblage in these rocks is .quartz + k-feldspar + garnet + cordierite (Joubert 1971, Moore 1983). To the north of the area, at Aggeneys and Gamsberg,- amphibolite-grade metamorphism is characterised by quartz+ biotite +muscovite+ sillimanite in metapelitic schists (Rozendaal 1978, Moore 1977). Calculations based on garnet-biotite geothermometry at Broken Hill and Achab (this study) provide temperatures compatible with M2 metamorphism at these localities viz. 650 °C at 4.5 - 5 kbar. Albat (1984) estimated pressure-temperature conditions of 700 - 900 °C and

-118-

40

35

30

25

20

8

6

4

2

0

+-' c Q)

8 0 ... Q)

a. 6

+-' ..c: Cl 4

Q)

~ 2

0

0·8

0·6

0'4

0·2

0

Figure 36:

ZnO /

FeO

MgO

MnO core rim rim rim

a b

Zoned pro iles across gahnite grains. (a: from centre to rim, b: from rim, accross central vein of blue gahnite, to rim) Distance etween individual analyses, (dots on diagram), is equivalen to 50 um.

-119-

" . ~ . ; .·

5 - 6 kbar in the granulite-facies terrane in the south. At Oranjefontein the the quartz+ k-feldspar + cordierite + sillimanite ± garnet and garnet + biotite + cordierite assemblages in the metapelitic rocks indicate that higher metamorphic grades were attained than at Aggeneys and Achab.

Garnet compositions are plotted as functions of their cation variability according to a method proposed by Sturt (1962) (Fig.37). Sturt (1962) showed that Fe and Mg content of garnet increases with increasing metamorphic grade. On Figure 37, it is apparent that garnet in the garnet-cordierite-biotite rock and the aluminous schist have similar Ca+Mn/Fe+Mg ratios and are representative of Sturt's (1962) sillimanite zone. Garnet associated with green gahnite in garnet-biotite rocks has similarly high Fe and Mg content whereas garnet occurring in blue gahnite-bearing assemblages and garnet partially replaced by retrograde chlorite are correlated with Sturt's (1962) ·biotite zone.

Analysed coexisting garnet-biotite and cordierite-biotite pairs from the metapelitic assemblages are plotted on an AFM diagram, (Fig.38). The crossing tie lines are explained in terms of a difference in bulk rock compositions of the two lithologies.

Geothermometric calculations were applied to the co-existing garnet-biotite and biotite-cordierite mineral pairs from the aluminous schist and metapelitic garnet-cordierite-biotite rock. Using the methods of Thompson (1976), Holdaway and Lee (1977), Ferry and Spear (1978) and Indares and Martingole (1985a) and a pressure of 4.5 - 5 kbar, based on the Mg/Fe ratio of cordierite, temperatures of 530 - 720 °C were calculated. Results are given in Table 22.

Maf ic rocks on the northern side of Vioolskraalberg, at the same stratigraphic horizon contain orthopyroxene-clinopyroxene assemblages. Geothermometric calculations based on coexisting orthopyroxene- , clinopyroxene pairs yield temperatures of 750 °C at 4.5 - 5 kbar (J. Mc Stay, pers. comm.). The mineral assemblages observed in the metapelitic rocks indicate upper-amphibolite- to granulite-facies metamorphism but temperatures obtained from biotite-garnet-cordierite geothermometry are variable (530 - 720 °C). The range of calculated temperatures suggests

-120-

1

' I

;

....

30 L..-

... ...... ....

0 20 c· I- BD ~ blue gahnite co + ~8 0 ~ "' 0 '

0

- ~ ~ <eJ:> ~ - green gahnite

Q& •• ~ • "·

10 I-

.:- 11 \

I . I I I I I I

10 20 30

wt% FeO + MgO

Symbols: dots : gahnite(+phlogopite, garnet) quartzites

circles : gahnite-bearing, garnet-biotite rocks -

closed triangles: garnet-, gahnite-bearing metaquartzite

open triangles : garnet-bearing metaquarttite

closed squares : garnet-biotite-cordierite schist

open squares : garnet-biotite rocks

I

Figure 37: Garnets plotted as wt% CaO+MnO vs. wt% FeO+MgO (after Sturt, I

1962).' . -121-

-

- -

F

Figure 38:

A

+quartz

+ k-feldspar

M

The aluminous schist (1) and metapelitic schist (2) plotted on an

AFM diagram.

-122-

Table 22: Results of garnei-biotite geothermometry on metapelitic rocks

from Oranjefonte n.

Method Employed Thompson Holdaway & Lee Ferry & Spear Indares & (1976) ( 1977) (1978) Martingole

(198Sa) * Sample Analysis

No.

JE 31 1 S87 S74 S60 S81

biotite- 2 627 609 S27 S16

garnet 3 641 621 S17 S02 4 S94 S80 SS3

JE 32 1 642 622 Sl6 474

biotite- 2 631 612 S2S S84

garnet 3 670 646 49S 471 4 628 719 S26 s SS9 sso S84 6 640 620 Sl7

JE 29 1 S68 biot-gar 2 S77

JE 29 1 S41 biotite- 2 S07 cordierite 3 SlO

4 633 s S99

JE 30 1 616 biotite- 2, 698 cordierite 3 632

MAXIMUM TEMPERATURES

JE 31,32 670 ±30 "C

JE 29,30,31,32 719 ±SO °C

JE 31,32 S60 ±30 °C

JE 29,31,32 S80 ±SO °C

* Calculations employing th~ different set of analyses

method of Indares and Martingole were done on a

-123-

that the retrograde metamorphic event resulted in some re-equilibration between Fe-Mg minerals in the metapelitic rocks. Temperatures of 650 -750 °C at 4.5 - 5 kbar, are compatible with the high-grade metamorhpic assemblages observed in the metapelitic rocks.

The presence of epidote-chlorite replacing garnet-biotite assemblages, chloritized biotite, garnet and widespread seritization/pinitization of feldspar and cordierite are evidence of a later low temperature, retrograde metamorphic event. Blue gahnite formation, in intergrowths with rutile, hematite and quartz replacing biotite, and in intergrowths with hematite and chlorite replacing garnet, is associated with this event. Quartz pegmatites associated with shearing at Vioolskraalberg are associated with this event (Joubert, 1971). Metamorphic conditions of greenschist facies are estimated (based on the presence of chlorite and epidote) with temperatures of less than 500 °C at pressures equal to or

' '

lower than that of the main metamorphic event at this locality.

The quartz-magnetite associations in the aluminous schist generally indicate fairly oxidising conditions during prograde metamorphism and hematite, (associated with blue gahnite) even higher f(0)2 conditions during retrograde metamorphism.

Quartz-magnetite-garnet-biotite assemblages in the metapelitic schist enable the application of Zen's (1985) BAMM buffer. Application of the buffer calculations indicate an average log f02 = -16.5 ±0.7 during upper amphibolite-granulite grade metamorphism (Table 23).

4.5.5 Gahnite Formation

Blue gahnite is fine-grained, occurring as aggregates of euhedral grains whereas green gahnite is porphyroblastic and may contain inclusions of quartz or biotite. Green gahnite is restricted in its occurrence to rocks at the contact of the aluminous schist and the overlying metaquartzite, whereas blue gahnite mineralization extend~ into the metaquartzite and garnet-rich rocks. Green gahnite is associated with prograde assemblages and it is proposed that green gahnite formed during the upper amphibolite grade metamorphic event.

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Table 23: Results of ox~gen fugacity calculations on Oranjefontein rocks.

JJ (3 ainalyses)

Corrections for substituJion in Biotite

Sample nr:

-4 log Xs1 0.1~ o.rn 0.18

-3 log XFe Ui 1.89

Corrections for substitu~ion in Garnet -3 log XFe a.sq

Average correction

Average correction

Average correction

Total correction

0.59i 0.59

Biotite 0.18

Bi ot i tie 1.79

Garnet 0.55

2.52

Average Correction = 2.46

(Sil

(Fe)

(Fe)

JE 32 (3 analyses)

0.19 0.18 0.17

1.59 1.66 1. 70

0.57 0.53 0.49

0.17

1.65

0.53

2.35

Reference BAMM buffer at 50 °C and 4.5 kb:

JE 29 (6 analyses)

0.19 0.21 0.24 0.24 0.18 0.20

1.64 1.42 1.66 1.64 2.03 1.48

0.63 0.67 0.65

0.21

1.65

0.65

2.51

Log f(0)2 = 10.29 - 26284/T + 0.148(P-1)/T ± 650/T = -18.97 ± 0.7

Corrected log f(0) 2 = -16.51 ± 0.7

-125-

The local presence of disseminated galena and rare chalcopyrite in the quartzites and presence of trace quantities of Pb and Cu in the bulk chemical analyses is supporting evidence for the presence of sulphides in the precursor sediments at Oranjefontein. The moblity of the Zn 2 + ion and its tendency to form colloids with Fe 2 + and OH (Wedepohl 1972) would result in desulphidation of sphalerite more readily than galena, which would account for the continued presence of galena in these rocks whereas only trace quantities of chalcopyrite and no sphalerite remain. It is proposed that the original sediments included a thin sulphide-bearing horizon between the precursor overlying quartzite horizons. with unusually Mn, Mg, Fe and

sediments of the metapelitic schist and the The sulphide-bearing horizon was associated

Al-rich sediments which under prolonged metamorphism to uppper amphibolite grades led to the formation of garnet, biotite, cordierite and green gahnite. A suggested prograde reaction is (Hicks et al. 1985): sphalerite + Mg-clay minerals -> green gahnite + biotite + garnet + quartz + S2 + H20

Minor but significant amounts of zinc were taken up by biot~ie during this reaction (ZnO up to 0.5 wt%). Segnit (1961) and Sandhaus and Craig (1986) proposed that, gahnite located in the peripheral regions of metamorphosed sulphide deposits and within metapelitic rocks where there is no association with sphalerite, may have formed by reactions involving zinc species adsorbed onto clay minerals or Fe/Mn oxides (Vine and Tourtelot 1970, Coveney 1979, Helios and Rybicke 1985). The presence of postulated clay minerals and significant concentrations of manganese in the proposed precursor lithologies at Oranjefontein may indicate that some zinc initially occurred adsorbed onto these components. The high levels of zinc, relative to iron, manganese and magnesium, in the gahnite-bearing quartzites, however, make it unlikely that all zinc could have been accomodated in this manner (Hicks et al., op. cit.).

Mineralogical and textural evidence for the formation of near end-member blue gahnite indicate that it formed during a period of retrograde metamorphism of greenschist grade subsequent to the formation of green gahnite. Low-temperature metamorphism accompanied by a fluid phase resulted in the breakdown of garnet and biotite and resulted in the formation of blue gahnite, chlorite, epidote and sericite.

-126-

Dietvorst (1980) proposed the formation of gahnite during retrograde breakdown of zinc-bearing biotite to form chlorite. In this process zinc is transferred from biotite to gahnite and does not enter the chlorite structure. At Oranjefontein, retrograde chlorite contains more zinc than biotite (3.9 wt% as opposed to 0.4 wt%) and this process cannot apply to blue gahnite formation. It is proposed that biotite, garnet and green gahnite participated in the retrograde, blue gahnite-forming reaction. The proposed retrograde reaction is; (Zn,Mg)green gahnite + Mg-biotite + garnet + quartz + H20 -> blue gahnite + chlorite + rutile +hematite+ sericite ••• Hicks et al. (op. cit.). The retrograde blue gahnite assemblages generally contain abundant quartz and very little sericite, which suggests this reaction was accompanied by addition of Si0 2 to and removal of K from the system.

-127-

5.1 Gahnite Mineralogy \

Chapter 5. CONCLUSIONS

Figure 2 showed that the stratigraphic successions at Swartkoppies, Broken Hill and Oranjefontein are similar and are correlated with the Bushmanland rocks of the NMC. At Swartkoppies and Achab, gahnite is associated with aluminous rocks and schists. At Oranjefontein, green gahnite occurs in garnet-biotite rocks in the uppermost horizons of the aluminous schist. Gahnite occurs in greater quantities in the metaquartzites at Achab and Oranjefontein. At Broken Hill gahnite occurs in the sulphide-bearing BIF rocks which occur below the massive quartzites.

Figures 39, 41, 42 and 43 sum~arise the analytical data on gahnite and spinels in the study areas.

Figure 40 (from Spry, 1984), results from a compilation of gahnite compositions as related to host rock lithology. Results of this study indicate that close to endmember blue gahnite from Oranjefontein is associated with a low grade metamorphic overprint which was associated with shearing and the emplacement of quartz veins (pegmatites} at this locality. Spry's diagram shows that gahnite of this composition generally occurs in association with pegmatities. Mg-rich gahnite is generally associated with marbles, however the Zn, Mg-rich composition of green gahnite at Oranjefontein is attributed to formation from ZnS-bearing, Mg-rich precursor clays. Gahnite composition from Achab and the massive sulphide deposit at Aggeneys is typical of gahnite associated with metamorphosed massive sulphide deposits (Fig.40). Achab is geographically close to the Aggeneys-Gamsberg ore body and it is proposed that gahnite formed in these rocks during prograde metamorphism of precursor ZnS-bearing metasediments. Gahnite in the highly aluminous rocks at Swartkoppies has a compositional range typical of those occurring in aluminous metasediments (Fig.40).

From Figure 39, it is apparent that gahnite compositions vary significantly between the study localities. Gahnite from Aggeneys is

-128-

\

SPIN EL

Figure 39:

GAHNITE

'tP D ljj1 D

.rEfoD D

Cb

0

• A

~ •

A D 0 .tt,..

D

DD c:Pt\3J

s: squar s dots c ire l s trian les:

Oranjefontein Aggeneys/Broken Hill Achab Swartkoppies

• • • •

•

HERCYNITE

Gahnite fr1m the study localities plotted on a triangular

endmember_ jli agram.

-129-

Gahnite

pegmatite I==::! metamorphosed massive

sulphide deposits aluminous metasediments

IS~ marbles

--

Spinel Hercynite

Figure 40: Compositional fields of g~hnite according to host rock lithology

(from Spry, 1984).

-130-

0 c:

N

40

30

20

10

0

Figure 41:

•

• •

• 0 ...

...... 0 • •

10 20

wt% FeO

Sym ols: squlres dod

• I l cir~ es . tri~ngles:

Oranjefontein Aggeneys/Broken Hill Achab Swartkoppies

• • •

30

Gahnite compositions from the study l-0calities, ZnO/~eO.

-131-

\

0 c:

N

* .... ::

• . ~ 0 • • 0

30 • ·:ct& I oa

D 0 12io D 0 B B • f2J cog,~ • 6'6Cb r:Poo ~D \ o• aa o• •

• 20 •

,; • ...

J;• • •

20 • • •

0 2 3 4 5 6 7 8

wt% MgO

Symbols: squares Oranjefontein dots Aggeneys/Broken Hi 11 circles Achab triangles: Swartkoppies

Figure 42: Gahnite compositions from the study localities, ZnO/MgO.

-132-

'

Figure 43:

1 . ' . I ' ' -..

... D fl . .. .

.. fferr -Cll

I&. -+0.5 .. ~ oitf

Cl

~ Cl

:E ...

..

0

-e\

•• D D ; J!>-.. ···J!-'1 ·: .. "191• :y. ~ ~-• • .. @

0·5 Zn/; Zn+Fe

Symbcls: squa~~es : Oranjefontein small dots: Aggeneys/Broken Hill larg dots: Achab tria~gles : Swartkoppies

1

Gahnite compositions from the study localiti~s,

I Mg/Mg+Re vs. Zn/Zn+Fe.

-133-

"

Zn-rich, Swartkoppies is Fe-rich and from Achab has a composition intermediate between these two. Green gahnite from Oranjefontein is relatively Mg-rich compared to Achab, but has similar Zn content. Blue gahnite from Oranjefontein is extremely Zn-rich and has almost no Mg component. Figures 39, 41 and 42 show almost complete solid solution between Zn, Fe and Mg components in spinel. Most of this is attributed to variation in bulk chemistry of the precursor sediments. At Aggeneys and Achab, Mg-rich gahnite occurs in the amphibole-,gatnet-bearing quartzite and garnet-gedrite schist whereas hercynite and Fe-gahnite occur in the magnetite quartzite and aluminous schist. Variation in zinc content of gahnite appears to be controlled by f(0) 2 , f(S) 2 and temperature during gahnite form~tion. of the sulphide associated retrograde blue gahnite.

This is shown by the relatively high Zn content gahnite and extremely high Zn content in the

5.2 Appraisal of zinc in minerals associated with gahnite

In metamorphosed rocks close to mineralised terranes staurolite is commonly cited as a zinc~bearing mineral and possible precursor to gahnite formation e.g. Atkin (1978), Stoddard (1979), Spry (1982a), Schumacher (1985). To a lesser extent zinc-bearing micas such as muscovite (Frondel and Ito, 1975), biotite (Frost 1973, Plimer 1977, Dietvorst 1980) and chlorite (Frondel and Ito 1975, Dietvorst 1980) are reported. In gahnite-bearing lithologies in Namaqualand staurolite is uncommon although it is reported to occur in association with gahnite at Gamsberg (Spry and Scott, 1986b). However, muscovite, biotite and chlorite are common in gahnite-bearing assemblages in all lithologies. All of the micas were analysed for zinc and also sillimanite, garnet and magnetite in view of their possible participation in gahnite-forming reactions. No zinc was found to occur in garnet or sillimanite and is attributed to the tendency for zinc to prefer four-fold co-ordination with oxygen in minerals.

Zinc in mica The open structure of mica allows a fairly free range of substitution into octahedral sites and due to similarity in ionic radii it is possible that zinc may substitute for iron, magnesium or manganese in the structure. A

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zinc-bearing muscovite, hendricksite, containing in excess of 20 mo1% ZnO is described by Frondel and Ito (1975). Prograde and retrograde muscovite was analysed in gahnite-bearing assemblages from Broken Hill and Achab. However, none contained significant zinc (> 0.2 wt% ZnO).

Zinc-bearing biotites are mentioned by Plimer (1977) in association with sulphide mineralization at Broken Hill, Australia and in the Scandinavian Caledonides at Kemia by Dietvorst (1980). Dietvorst (op. cit.) suggests that biotite, at amphibolite grades, is able to absorb small quantities of

• zinc, but that at lower temperaratures, zinc is less stable in the biotite structure. At Achab, amphibolite-facies biotite contains up to 0.35 wt% ZnO. In the' gahnite quartzites at Oranjef9ntein small biotite laths, armoured by quartz, and containing up to 0.4 wt% ZnO formed during prograde metamorphism of upper amphibolite grade.

Although chlorite is a common constituent in rocks associated with . I

metamorphosed massive sulphide deposits it has seldom been analysed as a potential zinc-bearing mineral (Frondel and Ito, 1975). At Oranjefontein, pervasive retrograde metamorphism has caused the alteration of biotite and garnet to chlorite in many of the rocks. Extensive analyses made on chlorites indicate a percentage of zinc in most chlorites. In garnet-bearing quartzites and garnet-biotite rocks containing blue gahnite, retrograde chlorite contains an average of 1.4 wt% ZnO and locally up to 3.5 wt% ZnO.

Zinc in magnetite In magnetite, zinc and aluminium may substitute for Fe 2 + and Fe3 +

respectively (Wedepohl 1970, Deer et al. 1980). In rocks of the NMC: magnetite-hercynite09 is common, and at the gahnite-bearing localities the hercynite commonly incorporates a minor gahnite component. It is probable that at the high metamorphic grades which prevailed in the NMC, a small amount of zinc was contained in the original magnetite-hercyniteas phase.

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5.3 Compositional zoning in spinels

Zoning in gahnite in quartzitic rocks .

Compositional zoning in gahnite in quartz rich environments has been reported from some localities and is generally accepted to result from re-equilibration of spinel in response to changes in temperature (Dietvorst 1980, Tulloch 1981, Sandhaus 1981, Treloar et al. 1981, Spry 1984, 1986, 1987b). Increasing zinc and decreasing iron and to a lesser extent magnesium, from core to rim, is the most commonly reported pattern and is attributed to gahnite formation under conditions of decreasing temperatures (e.g. Dietvorst 1980, Tulloch 1981, Spry 1984, 1986, 1987b). The opposite trend of decreasing zinc from core to rim is less common (Sandhaus 1981). Several workers (e.g. Frost 1973, Dietvorst 1980, Tulloch 1981, Hicks et al. 1985) observe that hercynite, unstable in the presence of quartz below 750°C, is stabilized at lower temperatures by increased incorporation of zinc into its structure.

Gahnite-bearing quartzites occur at Aggeneys, Achab and Oranjefontein. At Aggeneys the gahnite-bearing quartzite contained amphibole and garnet but gahnite is very fine grained and is not compositionally zoned. Similarly in the Dabiepoort quartzites, gahnite is fine grained and homogeneous. Gahnite-bearing quartzites at Achab contain coarse, poikiloblastic gahnite with numerous inclusions of quartz and these too are not zoned. Green gahnite in Oranjefontein quartzites occurs as coarse porphyroblasts, is commonly embayed to quartz and occasionally has quartz inclusions. Blue gahnite commonly occurs as a rim surrounding the green gahnite and also as tiny euhedral grains in the quartz matrix. A compositional profile across . . a rimmed gahnite grain (Fig.36), shows the sharp compositional break between green gahnite and blue gahnite. The compositional break coincides with an abrupt change in colour from a green central core to the blue rim, but individually the two varieties of gahnite are homogeneous. This compositional change is not considered to be a growth zonation but represents an overgrowth in response to widely differing metamorphic conditions which result in the original green gahnite being out of equilibrium in the quartzites. Many of the gahnite-bearing rocks contain garnet and analysis of core - rim compositions of garnet in gahnite- and non-gahnite-bearing lithologies did not reveal a consistent zonation pattern.

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Zoning in gahnite associated with Fe - Mg aluminosilicate minerals

Zoning in spinels in aluminous metasediments has been attributed to the partitioning of zinc, iron and magnesium between spinels and adjacent ferromagnesium aluminosilicate (Spry 1984, 1987b).

At Oranjefontein, in garnet-biotite-gahnite-quartz rocks, green gahnite occurs in direct contact with all three phases. However, even in this case the gahnite was homogeneous. Occasional grains 6f green gahnite in massive garnet rocks and garnet-biotite rocks were similarly unzoned. At Achab gahnite in contact with biotite and garnet in metapelitic schists did not show any zonation pattern. Gahnite in the massive gahnite rock at Swartkoppies and to a lesser extent, in the gahnite- and biotite-bearing fibrolite rocks at this locality showed some colour zonation, with dark green cores and pale green rims. The massive gahnite rock showed the most obvious colour zonation and this corresponds with an increase of 2.2 mol% gahnite and decrease of 1.7 mol% hercynite and 0.5 mol% spinel from core to rim (Fig.44). The gahnite-, biotite-bearing fibrolite rock showed the least compositional zoning at this locality. None of the biotite in rocks from Swartkoppies contained zinc and it is unlikely that the slight compositional zoning results from Fe-Mg exchange. It is also difficult to explain why the most dramatic zoning at this locality should occur in the massive gahnite rocks. In the absence of any suitable mineral for Fe-Mg exchange and the absence of sulphides for f(S)2 - f(0)2 controlled equilibria between gahnite and sphalerite, the zoning is attributed to gahnite growth during a period of decreasing metamorphic temperatures.

Zoning in gahnite associated with sulphide minerals

In metamorphosed massive sulphide deposits, Spry (1984, 1987b) has observed composftional zoning in gahnite and associated sphalerite. This he attributed to the partitionina. of Zn and Fe in response to changing f (0) 2 - f (S) 2 conditions between the two phases and associated pyrite/pyrrhotite. In this study coexisting gahnite and sphalerite were observed in the massive sulphide rocks and sulphide-bearing BIF from Broken Hill.

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I

'

:

I

26 I- 19

I - I / .,,..-24

/ 18 / / ....

ZnO ZnO 23 17

' 17 L.

23

"'""' '

16 .... '-...... 22 - \ 15 21 -

~ "" 14 20

FeO FeO 13 19 -c:

GI 4 4 u .. GI c. 3 3 -.___ - -- -.c: Cl 2 -- - 2

GI

3: 1 1

MgO MgO 0 0

' 0·4 0·4

0·3 0·3 --- ""-- "'-0·2

--~ 0•2

·-O•I 0•1

MnO MnO 0 0

a b

Figure 44: Core-rim analyses of gahnite from Swartkoppies in a; the massive

gahnite rock and b; the gahnite-biotite~fibrolite rock.

. -138-

'

Spry (1987a) observes that gahnite from Aggeneys is commonly colour zoned, this being attributed to the fine inclusions of secondary sphalerite, but only observed compositional zoning in gahnite enclosed in magnetite in the quartz-magnetite lithology. Here gahnite showed up to 18 mol% decrease in gahnite content with a corresponding increase of 14 mol% hercynite, 3 mol% galaxite and 2 moll spinel. He attributed this to depletion in zinc during gahnite growth. In this study it was found that gahnite in the massive sulphide rocks from Broken Hill is generally fairly fine grained and most commonly unzoned, however, one exception does occur. In a quartz-rich massive sulphide rock, gahnite coexists with quartz and muscovite in the gangue and sphalerite in the massive ore. Figure 45 shows an increase of 0.7 wt% ZnO and decrease of 0.5 wt% FeO and 0.2 wtl MgO between core and rim in two of the coarsest gahnite grains. The associated muscovite did not contain zinc and the association of gahnite and sphalerite suggest that Zn/Fe partitioning between the phases has . resulted in minor zoning.

It appears that there are various possibilities for gahnite zonation. Some of these are summarised below: 1. Re-equilibration of gahnite in quartz-rich rocks in response to

changing metamorphic temperatures due to the incompatibility of. iron-rich spinels and quartz below granulite grades of metamorphism.

2. Zn-Fe-Mg exchange between gahnite and associated Fe-Mg aluminosilicate minerals at amphibolite grades of metamorphism.

3. Zn/Fe partitioning, controlled by f(S)2 - f(0)2 equilibria between gahnite and sphalerite, pyrite/pyrrhotite in metamorphosed massive sulphide deposits.

4. A further possibility is the apparent sensitivity of gahnite composition to changes in metamorphic f(0)2• Moore and Reid (1987 in press) observed that fine-grained, disseminate gahnite in a gahnite­bearing quartzite shows significant compositional changes which can be related to its proximity to oxidising metamorphic fluid pathways.

Results from this study are thus not entirely consistent with documented I

occurrences of zoned gahnite. In this study it was found that gahnite in quartzites and quartz-rich rocks are generally not zoned, however this may be due in part to either fine grain size of gahnite or the extremely

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/

34 4

/ / 33 3r,

32 2

.___ ---31 ZnO MgO

30 0

+-' c ·Cl> 9 '- 0·8 -0 .... Cl> a. 8 '"- 0·6 -

" .__

+-' ~ -.c

C> 7 '- 0·4 -

Cl> :: 6 - 0·2 - MnO FeO

5 0

Figure 45: Core-rim compositions of gahnite from Broken Hill.

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poikiloblastic habit. In association with ferromagnesiun aluminosilicate minerals such as garnet or biotite, no consistent compositional zonation was observed in gahnite. At Swartkoppies, in massive gahnite rocks, colour zonation is associated with minor but consistent compositional zoning exhibited by increasing zinc and decreasing iron and magnesium from core to rim. This is attributed to a re-equilibration in response to changing metamorphic temperatures during the growth of gahnite. Compositional zoning, although present, was less obvious in the gahnite-, biotite-bearing fibrolite rocks from Swartkoppies. In the metamorphosed massive from Broken Hill only one rock contained zoned gahnite and in this rock gahnite is in contact with quartz and sphalerite. Here the zoning is attributed to Fe/Zn exchange between gahnite and sphalerite as proposed by Spry (1984, 1987a).

. 5.4 Gahnite in relaiion to Pressure, Temperature, and f(0) 2

Wall and England (1979) suggest that the hercynite content of zincian spinels is buffered by equilibria such as; 3FeA1 204 + 5Si02 = Fe3Al 2 Si301 2 + 2Al2SiOs and suggest that this reaction may be useful as a sliding geothermometer in conjunction with accurate geobarometry. Bohlen et al. (1986) did experimental reversals on this reaction and found that the equilibrium is located at 5.2 - 5.4 kbar at 880 °C and that it shifts to higher pressures with increasing temperatures. The incorporation of additional components of Zn or Fe3+, in hercynite broadens the stability field of hercynite-quartz and shifts the equilibrium to higher pressures.

Gahnite-quartz associations are found in granulite-, amphibolite- and greenschist facies parageneses in Namaqualand, indicating stability over a range of metamorphic conditions. Frost (1973), Kramm (1977) and Spry (1984) observe that gahnite in quartz-rich terranes is.stabilised by increased incorporation of zinc into its structure u~der decreasing metamorphic temperatures. This theory is supported to some extent by the study of gahnite in Namaqualand. Figure 46 shows gahnite compositions in the quartzites. Gahnite in quartz-rich assemblages at Oranjefontein contains 50 - 65 mo1% gahnite at upper amphibolite to granulite grades and

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I

in excess of 90 mol% gahnite at greenschist grades. Gahnite in quartz-rich assemblages at Achab and Aggeneys contains SO - 7S mol% gahnite at upper amphibolite grades (Fig.46).

Siefert and Schumacher (1986) suggest that the composition of the (Mg-Zn-Fe 2 +) spinel coexisting with cordierite and quartz may be sensitive to changes in pressure and investigated a geobarometer based on the reaction; Mg2Al2Sis01a = 2MgA1204 + SSi02. No such assemblages occur in the study area and this reaction could not have taken place. There does, however, appear to be some correlation of Mg content of gahnite with pressure and temperature. Figure 39 shows that gahnite and pleonaste in the granulite facies at Oranjefontein has in excess of 20 - 3S mol% spinel and SO - 60 mol% spinel respectively (T = 6SO - 7SO °C, P = 4.S - S kbar). Gahnite and zincian hercynite from Aggeneys, Achab and Swartkoppies at upper amphibolite grade metamorphism has between Sand 20 mol% spinel (T = 6SO - 670 °C, P = 4.S - S kbar). The composition of blue gahnite from which Oranjefontein formed during low temperature retrograde metamorphism contains less than 1 mol% spinel. The variation in gahnite-bearing assemblages does not support a spinel-quartz­aluminosil icate reaction, in which case the increase in mol% spinel content of gahnite with metamorphic temperature and pressure should be viewed with caution. However additional data may well yield more conclusive results in Namaqualand.

In some assemblages in the rocks studied, gahnite and garnet coexist stably although quartz and aluminosilicate are not necessarily part of the same paragenesis. Spry (1984, 1987a) and Spry and Scott (1986a) have suggested that gahnite may form by garnet breakdown in a solid-solid reaction i.e Fe3Al2Si3012 + ZnS + S~ -> ZnAl204 + 3FeS + 3Si02 + 02• Using the diagram suggested by Sturt (1962), garnet compositions were plotted as a function of Ca+Mn/Fe+Mg, (Fig.48). The hercynite content of gahnite associated with particular garnet-bearing rocks has been added to the diagram. Figure 48 shows an increase in hercynite content of gahnite with increasing Fe+Mg of garnet. There is, however no conclusive evidence for garnet-gahnite type reactions and Fe-Mg exchange is the most likely cause for this correlation between mineral phases.

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I I

I I

I

SPINEL

Figure 46:

GAHNITE

I I

I I

I I ./ I

I /" I • • I I .. I

I I

•1 I I /~ I I

/~lfi/ I

I ' I I

0/ I I I I

I I I

I I I I I I I I

I I I I I

I I I I I I

I I I I

I I I I

I I I I

I I I I

I I I I

I I I I

I I I

I I I

I I I

I I I

HERCYNITE

Gahnite compositions from gahnite quartzites at Oranjefontein (squares), Aggeneys (dots) and Achab (circles), plotted on an

endmember diagram.

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p kb

T°C

Figure 47:

6

5

4

3

2

600°C

contours of

log '02

23 2119 17 15

0·5 0·6 0·7 0·8 0·9

X ZnAl2 o4

2 kb 700 "'-11

600

500

contours

log '02

-23-21 -19

0·5 0·6 0·1 0·8 0·9

x ZnAl2 04

13

-17

Variation of gahnite composition with pressure and temperature

(from Spry, 1984).

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30

0 20 c :ii! + 0 cu 0

~ -~ 10

Figure 48:

)

5~3 ,26

14~<lb 15~~

~33 16

~40

10 20 30

wt% FeO+ MgO

The average hercynite content of gahnite (numbers) plotted alongside garnet from Aggeneys (horizontal stripe), Achab (cross hatch), and Oranjefontein (vertical stripe). Diagram after Sturt, 1962) .

. -145-

Spry and Scott (1986a) found that the composition of spinels in equilibrium with sphalerite and pyrite/pyrrhotite become more Zn-enriched with increasing f(0) 2 and f(S)2 and can be used as a measure of f(0) 2 during metamorphism (Fig.47). This, most probably is the cause for variation in Zn content of gahnite in the massive sulphide rocks and sulphide-associated BIF's at Aggeneys (Fig.39). A similar variation was observed in gahnite in sulphide-bearing rocks in the Mineral District, Virginia (Sandhaus 1981, Craig 1983) and Broken Hill, Australia (Pli~er, 1977).

The variation in Fe-Mg content of gahnite (Fig.39) may in part be attributed to variation in bulk rock composition ie. Mg-rich rocks at Oranjefontein, Fe-rich rocks at Aggeneys, Achab and relatively Fe-rich rocks at Swartkoppies. In garnet-biotite rocks at Oranjefontein and the metapelitic schists at Achab, gahnite composition may be further affected by Fe-Mg exchange between gahnite and garnet or biotite. Hercynite-quartz reacts to form garnet and sillimanite i.e. 3FeA120a + 5Si02 = Fe3Al2Si3012 + 2Al2SiOs as shown by Richardson (1968), Wall and England (1979) and Bohlen et al. (1986). Along with oxidising metamorphic fluids, the instability of (Zn-)Fe-Mg green gahnite and quartz caused formation of almost endmember blue gahnite in quartzites at Oranjefontein. Moore and Reid (1988 in press) have shown that gahnite composition may vary substantially even on the scale of centimeters according to its relative proximity to oxidising metamorphic fluid pathways. Gahnite­quartzites at Oranjefontein compared to Achab have undergone relatively higher grade metamorphism.at similar oxygen fugacities, (calculated log f(0) 2 is -16.02+/-0.7 in metapelitic rocks at Achab and -16.51+/-0.7 at Oranjefontein), yet have similar Fe and Zn content (Fig.40), so it would seem that prevailing metamorphic f(0)2 rather than temperature is th~ determining factor for gahnite composition in similar rock types where Zn-Fe-S equilibria and Fe-Mg exchange can be discounted. At Swartkoppies the 30 mol% variation in gahnite component is also attributed to changes in f (0) 2 rather than temperature. In these rocks, despite the presence of biotite, there is very little variation in Mg-Fe content of gahnite. It appears that gahnite exhibits a range of compositions in the amphibolite grades, whereas in the greenschist facies, e.g. the blue gahnite at Oranjefontein it has a narrow compositional range.

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It is concluded by this study that spinel composition is affected by bulk composition, Fe,Mg,Zn exchange between gahnite and co-existing silicate, sulphide or oxide minerals, metamorphic f(0)2 and temperature. In different lithologies which have been subjected to any one or a combination of these parameters, gahnite compo~ition will be dependent on the dominant parameter or a dominant combination of parameters. The affect of bulk rock composition and mineralogy will determine gahnite composition during initial growth. However, f(0) 2 and temperature apply strong constraints on gahnite composition in gahnite-quartz assemblages and f (0) 2 - f (S) 2 conditions in gahnite-sphalerite-pyrite assemblages.

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5.5 Gahnite in exploration

One factor which emerges from this study of gahnite is that on a regional scale gahnite may have substantially variable composition in rocks qf the same genetic sequence and occurring at similar stratigraphic levels. Similar studies of gahnite associated with sulphide mineralization in the Mineral District, Virginia (Sandhaus 1981, Craig 1983 and Sandhaus and Craig 1986) and Broken Hill, Australia (Plimer, 1977) show a far more restricted range of gahnite composition. This has significant implications on the use of gahnite composition as a guide to mineralization in Namaqualand. Sheridan and Raymond (1977), Karlsson et al. (1980) and Craig (1983) have commented on the association of gahnite with zinc mineralization and its potential for use in exploration. Spry (1984, 1986) and Spry and Scott (1986 a,b) found that gahnite associated with metamorphosed massive sulphide deposits has high zinc and iron contents and low magnesium contents. Bernier et al. (1984) found that the Zn/Zn+Fe+Mg ratio of gahnite associated with staurolite could be related to their proximity to mineralised zones and similarly Ririe and Foster (1984) suggested that the association of gahnite and sillimanite could be used as a directional indicator for sulphide mineralization.

The results of this study indicate that gahnite forms in aluminous terranes during regional metamorphism if zinc is present in the form of sulphides or as a constituent of the precursor sediments. According to Figures 39 and 40, there is some confirmation for Spry's (op. cit.) theory, in that gahnite occurring in aluminous sediments has more variable composition than gahnite associated with sulphides which tends to be richer in zinc and iron and has low magnesium contents. However this study does indicate a potential for compositional variation in gahnite which can be attributed to factors other than Zn-Fe-S equilibria. This must be taken into account if gahnite composition or gahnite-bearing assemblages are to be used as indicators for sulphide mineralization.

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(

5.6 Implications for mineralization in the Bushmanland rocks

It is generally considered that rocks of the Bushmanland sequence at Aggeneys and Gamsberg are sedimentary and reflect a continental, shallow marine depositional environment (Moore 1977, 1980, Rozendaal 1982). The Namies Schist is considered to have formed by deposition of (illitic and kaolinitic) clays and elastic material in shallow water in a large basin (Moore 1977, 1980, Rozendaal 1982). The overlying massive quartzite unit is thought to represent mature, quartz-rich sediment deposited in a shallow water, near shore, high energy environment (Rozendaal 1982). Reducing conditions are inferred by the presence of pyrite and pyrrhotite, while the presence of Pb, Zn and Ba in the quartzites suggest the influx of hydrothermal fluids (Rozendaal 1982). The iron formation at Aggeneys and Gamsberg is considered to have a submarine exhalative origin by Ryan et al. (1982) and Rozendaal (1982). However Moore {1977, 1986) interprets the siliceous, ferruginous and manganiferous rocks to result from chemogenic precipitation under hypersaline conditions in a restricted

. ' basin. Metamorphic textures exhibited by gahnite in relation to other minerals in gahnite-bearing assemblages in Namaqualand indicate that gahnite is metamorphic in origin. It is concluded that the precursor sphalerite was originally a costituent of the precursor sediments (e.g. black shales) and gahnite formed as a prograde mineral from sphalerite-bearing sediments in response to changing f(0) 2 - f(S) 2

conditions during ~iagenesis and metamorphism.

An implication from the presence of similar Mn-rich, sulphide-bearing sediments at Oranjefontein is that similar basins existed elsewhere in Namaqualand. This may have· implications for wide spread mineralization in the Bushmanland rocks.

If economic mineralizatio~ in Bushmanland rocks occurs in small basins, it may be necessary to exercise caution if the presence of gahnite in used as an indicator of sulphide mineralization. Gahnite appears to have formed readily where sulphides were part of the precursor sediments in a number of quartzites, metapelitic rocks and sulphide-bearing BIF in Bushmanland rocks in Namaqualand. However, gahnite is stable at the metamorphic grades which have affected Namaqualand rocks on a regional scale and persists in assemblages where all but traces of the precursor sulphides have disappeared.

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Deer1

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r

Plate 1. x25 s;ot;te-muscov;te-s;11;man;te­gahn;te sch;st, Achab. Prograde ·gahn;te (G) ;s assoc;ated w;th b;ot;te (B), quartz (Q) and s;11;man;te (S).

Plate 2. x25 s;ot;te-muscov;te-garnet-s;11 ;man;te sch;st, Achab. Small gra;ns of gahn;te (G) are assoc;ated w;th garnet (Ga) or occur as ;nclus;ons ;n b;ot;te ( B).

Pl ate 3. x25 Gahn;te quartz;te, Achab. Po;k;loblast;c porphyroblasts of gahn;te (G) ;n a banded gahn;te quartz;te.

••

' •

J · ,,-· -l" . ,. ...

. _. •

..

, ' ~ .

" ,.

' Q

...

' I

..

Plate 4. x25. Mass;ve gahn;te rock, Swartkopp;es. Note that the centre of the large grain ;s darker coloured than the ri111.

Plate 5. x25. Garnet-b;otite-gahnite-quartz rock, Oranjefonte;n. Green gahnite (Gg) ;s r;111111ed by blue gahn;te (Bg). e;ot;te (dark area) ;s replaced by hemat;te, quartz and blue gahn;te.

Plate 6. x25. Gahn;te (+phlogop;te, garnet) quartz;te, Oranjefonte;n. Green gahn;te (Gg) and b;ot;te (laths) breakdown to for111 blue gahn;te ( Bg) •

•. !' t

"· ., . .. £i

. • I:> ~

0

~ · c •• ·

*

Plate 7. x25. Gahn;te quartz;te, Oranjefonte;n. Green gahn;te (Gg) w;th blue gahn;te (Bg) r;ms. Specks of hemat;te outl;ne shapes, ;nd;cat;ng a precursor m;neral a~semblage •

Plate B. x25. Gahn;te quartz;te, Oranjefonte;n. 'Haloes' composed of specks of hemat;te outl;ne the former grain boundar;es of phlogop;te. Blue gahn;te (Bg) occurs ;n the haloes and also as aggregates assoc;ated with webbed hematite (dark m;neral).

Plate 9. x25. Gahnite quartzite, Oranjefontein. Euhedral blue gahnite crystals with a central circular area defined by a rim of hematite specks.

APPENDIX 1

ANALYTICAL METHODS AND PROCEDURES

All mineral analyses were done on the Cam~ca microprobe owned by the Geochemistry department of the University of Cape Town. The microprobe unit provides an online reduction of analytical data by the ZAF method. This was found to be inadequate for analyses of silicate minerals with high Fe contents e.g almandine, hercynite and so a method was built into the program whereby these analyses could be corrected for by the Bence

Albee (1968) method.

Operating conditions are outlined below:

Accelerating Voltage: 15 kV 25 kV for analysis of trace quantities of Zn in

. micas.

Beam Current: 40 nA 20 nA for micas.

The beam was focussed for analysis of all minerals except micas, for which

it was defocussed.

Counting Time:

Standards used:

10 sec 20 sec for Zn in micas.

Most of the standards are natural, IUGS approved standards. Zn (in sphalerit~) and Cr were analysed on sphalerite and chrome metal respectively. These standards have been tested by the Geochemistry Department at U.C.T. and are acceptable. Listed below are the standards used for analysis of

minerals.

MINERAL

Spinel, Magnetite

Micas, Amphibole

Epidote

Tourmaline

Garnet

Cordierite

Feldspar

Sphalerite

ELEMENT

Si Al Ti Mg, Cr Fe Mn Zn

Na, K, Si, Fe Ti Al, Mg, Ca Mn Zn

Si Ti Al, Cr, Fe, Mg Mn Zn

'Si,Al,Fe,Mg,Ca,Na,K Ti Cr Mn

Si, Ti

Al, Mg, Ca

Cr Mn Na

Si , Ti

Mg, Ca

Al, Fe Mn Na, K

Na, K

Si, Al

Fe, Mg Ca

Zn Fe, s Mn

\

STANDARD

Diopside Chrome, Gahnite Rut ile Chrome Chrome, Ilmenite Rhodonite Gahnite

Kakanui hornblende Rutile Kakanui pyrope,hornblende Rhodonite Zinc

Diopside Rut ile Chrome Rhodonite Zinc

Kakanui hornblende Rut il e Chrome

· Rhodonite

Kakanui pyrope Rut ile Chrome Rhodonite Kakanui hornblende

Diopside Rut ile Kakanui pyrope Rhodonite Kakanui hornblende

Nu nu Or-1 Kakanui hornblende La co

Sphalerite Sm-3 Rhodonite

Average below.

Si02 Ti02 Al203 Cr203 FeO MnO MgO CaO ZnO Na20 K20 F

Si02 Ti02 Ah03 Cr203 FeO MnO MgO cao ZnO Na20 K20

Zn Fe Mn s

lowest detection limit (LLD) of the elements in

Sp Mt

0.04 0.03 0.04 0.04 0.04 0.05 0.05 0.04 0.08 0.07 0.07 0.07 0.03 0.04

0.17 0.16

Fsp Amphi

0.06 0.04"

0.04 0.03 0.05 0.08 0.07

0.03 0.03 0.03 0.03

0.04 0.03 0.03 0.02

Sphalerite

0.05 0.03 0.03 0.03

Gt

0.04 0.04 0.04 0.05 0.08

-0.06 0.03

0.03 0.03

Tourm

0.04 0.04 0.04 0.04 0.07 0.05 0.02 0.03

0.03 0.02

Biot Muse

0.03 0.03 0.02 0.02 0.03 0.03 0.04 0.04 0.04 0.03 0.03 0.03 0.03 0.02 0.07 0.02 0.02 0.03 0.03 0.03 0.02 0.12

Epi Pyxm

0.04 0.05 0.04 0.05 0.03 0.04 0.04 0.05 0.03 0.07 0.03 0.06 0.03 0.03 0.03 0.03

0.04 0.04 0.03

the analyses are listed

Chl Crd

0.04 0.04 0.04 0.04 0.03 0.04

0.05 0.10 0.08 0.07 0.06 0.03 0.03 0.03 0.03 0.16 0.02 0.04 0.02 0.03

/

The electron microprobe is unable to distinguish between Fe 2+ and Fe3

+ . and all Fe is analysed as FeO (ie. Fe2+), This results in stoichiometric irregularities in minerals which incorporate significant quantities of Fe3+ in their structure. A method based on the stoichiometry of individual minerals has been included in the data reduction program to account for this, but it was found to be inadequate for iron-rich spinels and iron oxides. The most commonly used methods for recalculation of total FeO to FeO and Fe 203 are based on mineral structure, stoichiometry or charge balance. The method used here was suggested by Haggerty (pers. comm.) and does not require site occupancy assumptions. An example of a gahnite calculation is outlined below:

Wt% Atomic Mol No. No. Anions Cations I

oxide props. props. Cations Anions xl.7131 xl.7131

Si02 60.08 Ti02 79.90 Al203 58.iO 101. 96 0.5757 1.1514 1.7271 2.9587 1. 9725 Cr203 0.05 151.85 0.0003 0.0007 0.0010 0.0017 0.0012 FeO 7.75 71.85 0.1079 0.1079 0.1079 0.1848 0.1848 Fe203 159.69 MnO 0.38 70.94 0.0054 0.0054 0.0054 0.0093 0.0093 MgO 7.01 40.31 0.1739 0.1739 0.1739 .0. 2979 0.2979 Cao 56.08 ZnO 25.38 81.38 0.3119 0.3119 0.3119 0.5343 0.5343

Total 99.27 1.7512 3.9867 3.0000

Nr cations in gahnite = 3/1.7512 = 1.7131 Nr anions in gahnite = 4 4 - 3.9867 = 0.0133 0.0133 x 2 = 0.0266 •••• Fe 203 in formula 0.1848 - 0.0266 = 0.1582 ..•. FeO in formula Recalculate wt% FeO = 0.1582/1.7131 = 0.0923

0.0923 x 71.85 = 6.6351 Recalculate wt% Fe203 = 0.0266/1.7131 = 0.0155

0.0155 x 159.69 = 2.3553 2.3553/2 = 1.1777

Wt% oxide

58.70 0.05 6.63 1.18 0.38 7.01

25.38

99.33

...

! ,'

APPENDIX 2

EXPLANATION OF GEOTHERMOMETRIC AND OXYGEN FUGACITY CALCULATIONS

GEOTHERMOMETRY

On the basis of predicted phase r•lations in the system K20-FeO-MgO-Al203-Si02-H20 and available experimental and thermochemical data, Thompson (1976) provides a method to calculate isobaric T - X(Fe-Mg) sections. Predicted reactions involving garnet -biotite - cordierite - sillimanite - quartz with muscovite or K-feldspar are.compared with available experimental data and compositions of co-existing phases in natural assemblages. The equation: n ln Ko +~l:P/RT = if,/R + ~/R • 1/T provides a means of calculating temperature based on Fe - Mg exchange between garnet - cordierite' and garnet - biotite pairs (ln Ko= Fegar/Mggar.Mgb1ot/Feb1ot or Fegar/Mggar.Mgcrd/Fecrd

1:§,/R, ~/R for the exchange reactions are obtained from experimentally investigated reactions in pure Fe and Mg systems, ~/R is obtained from

available thermochemical data.

gar-biot Gar-Crd

b,V /R (deg bar-1) /§,/R -0.0234 -1.560 -0.0155 -1.896

&itR (deg) 2739.646 2724.948

Ferry and Spear (1978) did experimental investigations on the exchange reaction : Fe3Al2Si3012(almandine) + KMg3AlSi301o(OH)2(Phlogopite) = Mg3AL2Si3012(pyrope) + KFe3AlSi301o(OH)2(biotite). They determined the partitioning of Fe and Mg between. sythetic garnet and biotite at 2.07 kbar in the range 550 - 800 °C. At equilibrium&=~ - T~ + Pt!i + 3RT ln K = O. E_stmates of 6"H and f:f, are obtained from their experiments (4.662 e.u. and 12.454 cal) and~V is obtained from thermochemical data (0.057 cal/bar). It was found that at 2.07 Kbar and between 550 and 800 °C, ln (Mg/Fe gar I Mg/Fe biot) = -2109/T(K) + 0.782. The equation has a

resolution of ± 50 °C and provides a geothermometer without correction for components, (other than Fe and Mg), of up to 0.2 Ca+Mn/Ca+Mn+Fe+Mg in garnet and 0.15 (Alv 1 +Ti)/Alv 1 +Ti+Fe+Mg in biotite.

Departures from ideality in garnet due to substitution of Ca and Mn for Fe and Mg and in biotite due substitution of Alv 1 for Al 1 v, cause inconsistancies in geothermometric calculations in high grade (granulite facies) metamorphic rocks which are not present in the middle amphibolite facies. Using the experimental results of Ferry and Spear (1978), Indares and Martingole (1985a) provide a new calibrat1on which incorporates correction for substitutions in garnet and biotite. Two models, (model A, calculated with available thermodynamic data and model B, compiled from empirical data), are proposed to account for. deviations from ideality. The calibration T(K) = [12454 - 0.057P(bar) + 3(mXA1 + nXT1 biot) - (WcaXca +

WMnXMn gar)]/ 4.662 7 5.9616 ln Ko

where m = (WFaA1 - WMgA1 biot) = -4.464 (model A) = -1590 (model B) and

n = (WFeT1 - WMgT1 biot) = -6767 (model A) = -1451 (model B)

is based on Ferry and Spear's (1978) experimental method and gives results comparable with those of Thompson's (1976) calibration. Indares and Martingole (1985b) found that inconsistencies in geothermometric calculations in granulite facies rocks can be attributed to local variations in Ko values on the scale of a thin section, caused by late Fe - Mg exchange during cooling. This can be avoided by obtaining analyses from garnet cores and matrix biotite. In contrast, adjacent garnet - biotite grains or inclusions of biotite in garnet provide K0

values representative of some stage during cooling.

. ~· •·

GEOBAROMETRY

The stability field of cordierite in high-grade metapelitic rocks was determined experimentally by Holdaway and Lee (1977). The equations:

(1) 1.26 Fe crd + 0.84 K-fsp + (1-l.26n)H20 = 2.08 sill + 4 qtz (2) 2.52 Mg biot + 3 alm = 2.52 Fe biot + 3 py (3) 3 Fe crd = 2 alm + 4 .sill + 5 qtz + 3n H20 provide the basis for a geobarometer. Equation (1) takes place at 640 °C at 2 kbar and 710 °C at 2.7 kbar. Equation 2 takes place at 650 °c at 3.4 kbar and 760 °C at 2.9 kbar. At the temperature and f (H20) of interest the molar content of cordierite is given by n. The barometer is based on

the relation P V =-RT ln (XFe products/XFe reactants). Results of the experiments using this relation are:

P V = -2.52 RT ln [XFe biot/XFe crd] for reaction (1) ( V = -1.1519) and P V = -6 Rt ln [XFealm/XFe crd] for reaction (2) ( V = -2.7805)

OXYGEN FUGACITY CALCULATIONS

Zen (1985) developed an oxygen fugacity buffer curve based on the assemblage biotite - garnet - muscovite - magnetite - quartz which is applicable to peraluminous granites, schists and gneisses. The reaction: KFe3AlSi3012H20 (annite) + Fe3Al2Si3012 (almandine) + 02 <-> KAl 2AlSi3012H2 + 2Fe304 (magnetite) + 3Si02 (quartz) provides the base for the buffer system. Using thermochemical data and the equilibrium oxygen fugacity equation 2.303 RT log f(0) 2 = Gs(T0 ,l) + V(Pe-1) .••• where Gs, Vs= sum of G/V for the reaction phases. The equation applicable to endmember phases is log f(0) 2 = 10.29 - 26284/T + 0.148(P-1)/T ± 650/T =Reference buffer

curve.

Compositional corrections are necessary to account for: (i) annite - phlogopite solid solution and excess aluminium on

tetrahedral arid octahedral sites in biotite, (ii) aluminium distribution over the tetrahedral and octahedral sites and

excess Si in tetrahedral sites in muscovite, (iii) components of spessartine, pyrope and grossular in garnet. Taking into account the departures of biotite, garnet, and muscovite from

·their endmember formulae the BAMM buffer equation is: log f(0) 2 = 10.29 - 26284/T + 0.148(P-l)/T(K) - 4logXs1(biot) -3logXFe 2 +(biot) - 3logXFe 2 +(gar) + 2logXAlv 1 (musc) + 4logXSi(musc) +

(650/T - 1) This provides a buffer curve located between the hematite - magnetite and the magnetite-quartz-fayalite curves. Absence of biotite or almandine in the assemblage indicates higher oxygen fugacity and absence of muscovite or magnetite, lower oxygen fugacity than the buffer value. A biotite~garnet rock should not be stable with hematite.

APPENDIX 3

ENEMEM3ER CCM>QSITIONS OF Gl\HNITE (After stoichianetric recalculation for Fe 3T and slbtraction of magnetite COl'lp:)nent.)

ABN 12 ABN 12 ABN 12 ABN 12 ABN 13

ABN 13 ABN 14 ABN 14 ABN 14 ABN 14

ABN 16 ABN 16 ABN 16 ABN 16 ABN 16

ABN 3 ABN 3 ABN 4 ABN 4 A8N 4

S,YTl'bo l s : c : centre of grain r : rim of grain bl : blue gahnite (Oranjefontein gr : green gahnite (Oranjefontein)

Hercynite Spinel Gahnite 3).17 8.84 61.00 29.19 9.al 61.76 29.55 9.17 61.29 3).61 9.04 00.35 33.93 7.19 58.88

Hercynite Spinel Gahnite 29.33 8.29 62.39 26.97 7.50 65.52 24.46 7.46 E38.00 27.18 7.65 65.18 26.34 7.49 66.17

Hercynite Spinel Gahnite 33.15 6.90 59.94 34.26 6.00 59.66 33.12 6.86 00.02 34.03 6.62 59.36 33.72 6.61 59.67

Hercynite Spinel Gahnite 36.78 10.96 52.27 33.22 8.66 58.13 23.26 3.3) 73.43 33.96 5.90 00.14 34.67 5.83 59.50

Hercynite Spinel Gahnite ABN 13 33.04 7.59 59.37 ABN 13 28.29 7.63 64.00 ABN 13 32.61 7.69 59.70 ABN 13 32.14 8.20 59.66 ABN 13 32.26 8.22 59.52

Hercynite Spinel Gahnite ABN 14 26.10 7.66 66.24 ABN 14 25.00 7.36 66.83 ABN 14 25.82 7.3) 66.87 ABN 16 33.43 5.62 00.95 ABN 16 34.00 5.31 00.00

Hercynite Spinel Gahnite ABN 16 33.77 6.84 59.38 ABN 3 33.83 11.48 54.69 ABN 3 29.27 8.76, 61.89 ABN 3 25.25 9.93 64.82 ABN 3 33.45 9.62 56.93

Hercynite Spinel Gahnite A8N 4 31.39 5.77 62.83 ABN 4 32.17 6.11 61.72 ABN 6 42.29 25.61 32.00 ABN 6 36.43 34.03 29.54 ABN 6 19.64 6.14 74.23

Hercynite Spinel Gahnite Hercynite Spinel Gahnite ABN 8 21.13 6.11 72.76 ABN 8 19.38 6.21 74.41 ABN 8 20.65 6.22 73.13 ABN 8 19.45 6.3.) 74.24 ABN 8 20.15 6.13' 73.73 ABN 8 19.84 5.89 74.26 ABN 8 19.57 6.15 74.28 ABN 8 21.54 6.00 72.37 ABN 8 20.29 6.25 73.46 ABN 8 20.23 6.27 73.!:D

Hercynite Spinel Gahnite Hercynite Spinel Gahnite ABN 9 29.89 16.76 53.35 ABN 9 31.20 15.00 52.00 ABN 9 3.).66 17.12 52.22 ABN 10 28.57 9.38 62.aJ ABN 9 3.).46 15.46 54.07 ABN 10 25.85 10.00 64.07 ABN 9 31.47 14.65 53.88 ABN.10 . 16.47 8.01 75.52 ABN 9 31.03 14.95 54.03 ABN 10 19.87 8.73 71.40

Hercynite Spinel Gahnite Hercynite Spinel Gahnite ABN 11 32.21 6.71 61.00 ABN 11 c 36.57 7 .CJ3 56.38 ABN 11 35.43 7 ,(jj 57.53 ABN 11 r 36.88 7 ,(13 56.07 ABN 11 34.89 6.39 58.72 ABN 11 c 36.44 7.34 56.21 ABN 11 36.77 5.75 57.48 ABN 11 r 36.52 7.13 56.36 ABN 11 3.).a) 6.36 63.58 ABN 11 36.83 5.92 57.25

Hercynite Spinel Gahnite Hercynite Spinel Gahnite ABN 11 37.03 5.28 57.69 SK 2 c 38.89 8.59 52.52 SK 2 c 39.66 8.13 52.21 SK 2 r 38.33 8.82 52.85 SK 2 r 37.95 8.62 53.44 SK 2 c 37.93 8.78 53.29 SK 2 37.86 9.17 52.97 SK 2 r 38.31 9.13 52.57 SK 2 38.55 8.76 52.68 SK 2 37.12 9.16 53.72

Hercynite Spinel Gahnite Hercynite Spinel Gahnite SK 2 36.67 9.01 54.33 SK 3 56.41 14.98 28.61 SK 2 38.47 8.70 52.84 SK 3 55.98 15.00 28.93 SK 2 c 39.33 8.97 51.70 SK 3 c 56.49 15.54 27.97 SK 2 r 38.00 8.94 52.15 SK 3 r 56.47 14.91 28.62 SK 2 55.68 15.86 28.46 SK 3 c 56.15 15.03 28.82

Hercynite Spinel Gahnite Hercynite Spinel Gahnite SK 3 r 58.01 14.3.) 27.69 SK 3 55.67 15.39· 28.94 SK 3 c 56.3) 14.57 29.14 SK 4 49.22 12.aJ 38.72 SK 3 r 55.39 15.45 29.16 SK 4 c 48.29 11.54 40.17 SK 3 c 55.84 15.97 28.19 SK 4 r 48.35 12.33 39.32 SK 3 r 54.98 16.10 28.92 SK 4 c 47.22 12.76 40.02

Hercynite Spinel Gahnite Hercynite Spinel Gahnite SK 4 r 46.82 12.81 40.38 SK 4 c 47.55 12.34 40.11 SK 4 c 46.56 12.58 40.86 SK 4 r 46.00 11.98 41.22 SK 4 r 48.44 12.48 39.09 SK 4 c 35.aJ 7.53 57.41 SK 4 c 47.12 12.66 40.22 SK 4 r 37.52 8.00 54.40 SK 4 r 46.65 13.00 40.35 SK 4 36.92 8.14 54.94

Hercynite Spinel Gahnite Hercynite Spinel Gahnite BH 2 c 19.91 5.86 74.27 BH 2 18.89 5.76 75.36 BH 2 r 18.92 4.95 76.13 BH 2 18.99 5.77 75.25 BH 2 16.91 4.67 78.42 BH 2 c 19.27' 5.63 75.10 BH 2 18.24 5.47 76.28 BH 2 r 18.23 5.00 76.68 BH 2 17.86 4.96 77.48 BH 2 18.84 5.59 75.58

Hercynite Spinel Gahnite Hercynite Spinel Gahnite BH 2 15.79 4.35 79.85 BH WE 1 22.04 5.17 72.00 BH WE 1 22.10 4.92 72.98 BH WE 1 23.48 5.00 71.53 BH WE 1 21.58 5.11 73.31 BH WE 1 20.81 4.72 74.46 BH WE 1 24.27 4.38 71.35 BH WE 1 23.57 5.00 71.43 BH WE 1 22.63 4.51 72.85 BH WE 1 23.07 4.64 72.29

Hercynite Spinel Gahnite Hercynite Spinel Gahnite BH WE 2 25.79 4.72 69.49 BH WE 2 22.97 4.53 72.49 BH WE 2 23.27 5.C6 71.68 BH WE 2 22.92 4.54 72.54 BH WE 2 22.67 4.40 72.93 BH WE 2 22.64 5.C6 72.31 BH WE 2 26.26 4.83 68.91 BH WE 2 21.79 4.58 73.63 BH WE 2 28.41 4.76 66.83 BH WE 2 22.51 4.95 72.54

Hercynite· Spinel Gahnite Hercynite Spinel Gahnite Bl£ 3)2 54.96 9.28 35.75 BHl 3)2 67.22 10.03 22.76 131-G 3:>2 65.00 9.48 24.62 240 fJG 56 36.77 11.95 31.28 Bl£ 3:>2 62.21 9.67 28.12 240 fJG 56 39.39 12.02 . 48.69 131-G 3:>2 69.43 10.79 19.78 240 fJG 56 42.15 12.00 45.76 Bl£ 3)2 62.C6 11.52 26.43 240 fJG 56 28.07 11.97 56.96

Hercynite Spinel Gahnite Hercynite Spinel Gahnite 240 fJG 56 3:>.75 12.94 56.31 CFB 1 29.51 2.70 67.79 240 fJG 56 31.81 12.45 55.73 JE 2 bl 5.21 0.3:> 94.49 240 fJG 56 32.95 13.99 53.C6 JE 2 bl 4.92 0.3:>. 94.78 CFB 1 29.62 2.53 67.85 JE 2 bl 4.31 0.3:> 95.39 CFB 1 28.68 2.58 68.74 JE 2 bl 4.12 0.3:> 95.58

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 2 bl 3.92 0.40 95.68 JE 3 bl 3.54 0.61 95.86 JE 2 gr 15.18 21.26 63.56 JE 3 bl 3.12 0.40 96.48 JE 2 gr 16.65 21.12 62.37 JE 3 gr 17.02 23.81 59.17 JE 2 gr 15.10 21.28 63.63 JE 3 gr 16.62 24.29 59.59 JE 2 gr 16.25 20.38 63.37 JE 15 bl o.oo 0.3:> 99.70

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 15 bl 4.79 0.27 94.95 JE 15 bl 3.94 0.31 95.75 JE 15 bl 4.23 0.36 95.41 JE 15 bl 3.00 0.27 95.93 JE 15 bl 4.84 0.26 94.00 JE 15 bl 4.23 0.31 95.45 JE 15 bl 5.3:> 0.97 93.73 JE 15 bl 3.96 0.00 96.04 JE 15 bl 4.43 0.57 95.00 JE 14 bl 3.70 O.!:n 95.00

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 14 bl 3.01 0.3) 96.69 JE 18 bl 4.52 0.00 94.87 JE 14 bl 3.10 0.20 95.00 JE 18 bl 4.73 0.3) 94.96 JE 18 bl 4.25 0.3) 95.45 JE 18 bl 3.73 1.11 95.16 JE 18 bl 6.21 1.12 92.67 JE 18 gr 16.52 25.90 57.58 JE 18 bl 4.92 0.10 94.98 JE 18 gr 16.62 25.85 57.54

Hercynite Spinel Gahnite Hercynite Spine1· Gahnite JE 19 gr 15.32 3).87 53.81 JE 19 gr 13.38 3).70 55.91 JE 19 gr 10.96 33.45 55.59 JE 19 gr 13.32 3).29 56.39 JE 19 gr 17.13 29.59 53.28 JE 19 gr 13.46 29.83 56.70 JE 19 gr 14.51 31.14 54.35 JE 19 gr 12.29 29.69 58.01 JE 19 gr 14.88 3).44 54.68 JE 23 bl 2.70 0.70 96.00

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 23 bl 3.61 1.10 95.29 JE 23 gr 11.00 32.88 54.86 JE 23 bl 2.10 0.!:() 97.40 JE 23 gr 11.24 32.19 55.89 JE 23 bl 3.90 0.21 95.90 JE 23 gr 11.71 31.76 55.81 JE 23 gr 12.42 32.52 54.15 JE 23 gr 11.40 32.00 55.84 JE 23 gr 12.25 32.48 54.51 JE 23 gr 11.42 31.56 56.26

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 23 gr 11.72 31.17 56.37 JE 39 bl 2.73 0.61 96.66 JE 26 bl 2.22 0.10 97.68 JE 74 bl 3.44 0.55 96.01 JE 35 bl 3.83 0.00 95.57 JE 74 bl 4.36 0.49 95.15 JE 35 bl 3.76 0.41 95.83 JE 74 bl 3.33 0.45 96.22 JE 35 bl 4.26 0.41 . 95.33 JE 74 bl 16.92 26.52 56.56

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 74 bl 1.62 0.00 98.38 JE 84 gr 16.73 25.78 57.48 JE 74 gr 16.28 24.18 59.54 OF 7 gr 21.14 28.15 !:().71 JE 82 bl 1.46 0.52 98.03 OF 7 gr 18.94 21.88 59.18 JE 82 bl 3.19 0.77 96.04 OF 7 gr 21.05 27.19 51.76 JE 82 bl 3.18 0.66 96.16 JE 16 16.29 52.94 3).77

Hercynite Spinel Gahnite Hercynite Spinel Gahnite JE 16 19.29 56.91 23.00 JE A 45.18 53.89 0.93 JE 29 42.76 25.77 31.47 JE A 45.22 53.55 1.23 JE A 41.97 56.85 1.18 JE G 39.54 55.73 4.72 JE A 46.12 52.99 0.89 JE G 43.48 53.97 2.55 JE A 44.97 53.82 1.22 JE G 36.62 59.32 4.C6

Hercynite Spinel Gahnite JE G 41.75 56.07 2.17

AVERJIGE ENIMM3ER ro.roSITICNS Of OAA'JJEFOOEIN ~ET

SalqJle JE 32 JE 31 JE 29 JE 10 JE 36

UV 0.09 0.03 0.14 0.02 0.09 AD 0.03 0.05 0.04 0.23 1.81 GROSS 1.66 4.38 . 4.26 10.(.6 4.70 PYR 21.28 23.81 31.62 11.72 14.(.6 SPESS 10.98 7.03 4.87 40.07 39.03 ALM 65.97 64.72 59.CS 36.91 40.32

SalqJle JE 18 JE 82 JE 20 JE 14 JE 15

UV 0.00 0.01 0.03 0.03 '0.11 AD 0.07 0.96 0.63 1.09 2.04 GROSS 5.00 . 3.94 5.00 12.77 5.65 PYR 36.88 34.67 33.78 16.01 15.38 SPESS 23.34 24.95 33.41 51.17 54.94 ALM 33.92 35.48 27.07 18.93 22.00

List of rock types JE 31, 32 Metepelitic schists JE 29 Alt.minous schist JE 10 Quartzo-feldspathic gneiss JE 36 Garnet-biotite rock JE 35, 7 Altered garnet-biotite rocks JE 74 Gahnite quartzite JE'19, 18 Garnet-biotite-gahnite-quartz rocks JE·82 Gahnite-bearing massive garnet rock JE 20 Garnet-bearing rretaquartzite JE 7 Pierrontite-garnet rock JE 14, 15 Garnet-,gahnite-bearing rretaquartzite JE 3, 2 Gahnite quartzites

Abbreviatons: UV uvarovite AD andradite GROSS grossular PYR pyrope SPESS spessartine ALM almandine

JE 35

0.07 0.12 7.12

29.69 32.03 3).96

JE 3

0.02 0.12 6.02

31.92 21.79 40.14

JE 7 JE 74 JE 19

0.10 0.00 0.02 1.40 0.77 0.09 3.9) 3.52 5.93

19.00 32.32 34.03 3).00 3).13 26.77 43.00 33.25 33.17

JE 2 OF 7

0.03 o.oo 0.70 0.10 5.02 5.59

34.50 34.46 20.63 ~.61 33.54 39.27

APPENDIX 4.

Mineral Analyses

Electron microprobe analyses of minerals are listed in this

section. All Fe was analysed as FeO. Calculated Fe3 + is ~

included in the spinel, analyses.

nusCOUITE

SIOZ 42.55 4Z.74 42.76 43.17 42.68 42.33 43.08 43.71 42.98 44.24 TI02 1.6Z 1.60 1.47 1.57 1.59 L33 1.37 1.24 1.48 1.l3 ftl20l 32.34 31. 91 31.81 32.27 31.79 31.94 32.64 31.88 31.88 32.JO CR203 3.37 HO 2.92 3.37 4.04 2.60 3.10 2.97 Z.82 2.66 2.57 2.41 HHO .09 .09 .07 .OS .05 .07 .05 .14 .09 .05 nco 1.70 1.71 1.55 1. 70 1.70 1.63 1.58 1. 44 1.32 1.38 CAO .17 .23 Hft20 9.08 .23 .23 .21 .21 .17 .23 .43 .41 .48 1<20 9.38 9.22 9.42 9.23 9.20 9.23 9.63 9.47 9 .81 ZHO .04 till .15 .07 .13 .36

TOTAL 90.47 94.44 91 .40 91.14 90.42 89.77 91.36 ~1.13 90.Z2 92.00

~~ ftTOnlC PROPORTIONS BASED OH SELECTED HO. OF OXYGEHS """

OXYGEK 22 22 22 22 22 22 22 22 22 22

SI . 5.897 5.877 6.027 6.056 6.047 6.038 '6,034 6.137 6.092 6.143 TI .169 .165 .156 .166 .164) .143 .144 .131 .158 .139 AL S.283 5.172 5.285 5.336 5.309 5.370 5.389 5.276 5.327 5.287 CR .366 fE2+ .338 .388 .476 .305 .367 .354 .330 .312 .305 .280

"" .011 .010 .008 .006 .006 .008 .006 .017 . 011 .006 llG .351 .350 .326 .355 .359 .347 .330 .301 .279 .286 Cft .025 .035 HA 2.440 .061 .061 .057 .058 .047 .062 .117 .118 .129 K 1.646 1.658 1.686 1.668 1. 674 1.649 1. 725 1.713 1.738 ZH .004 .016 .007 .014 .037

sun 14. 513 14. 041 14.035 13. 982 13.992 13. 995 13.983 14. oi 6 14.002 14.008

1<1rl«lf SAnPLI DIRECTORY *"** SAnPLE HO. DESCRIPTION SAnPLf: HO. DESCRIPTION

---------- ----------- ---------- -----------1 BH-2 6 BH-2 2 BH-2 7 BH-2 J BH-2 8 BH L0-1 4 BH-2 9 BH L0-1 5 BH-2 10 BH L0-1

nuscouITE

SI02 44.00 45.30 411.27 44.32 43.16 44.04 45.51 43.59 45.72 45.26

TI02 .11 .59 1.71 1.72 1.71 1.79 .66 1. 76 1.32 1.08 AL20l 35.23 lS.50 35.7l 34.67 l4.83 35.19 37 .14 34.53 36.34 37.08 CR20l .05 .07 .05 .06 HO 1.05 1.83 .94 1.27 1.09 1.lS 2.10 .92 1.40 1.24 HHO liD .06 ltD .04 nGO .79 .34 .56 .62 .50 .65 .69 .64 .58 .48 CAO HA20 .72 .22 .80 .58 .62 .58 .52 .54 .62 .67 K20 9.40 7 .13 9.24 9.15 9.04 9.03 8.30 9.05 9.23 10. 07 ZHO .07 ND .05 . .14 HD

JOHil 91.32 CJO. 91 93.ZS CJ2.45 91.04 92.71 95.03 91.25 95.25 95.90

idt ATOnic PROPORTIONS BAS£D OH SEL£CTED HO. OF OXYGENS 1rfl

OXYGrH Z2 22 Z2 22 22 22 Z2 22 22 22

SI 6.080 6.188 5. 991 6.055 5.987 6.000 6.018 6.028 6.051 5.979 TI .011 .061 .174 .177 .178 .183 .066 .183 .1l1 .107 AL 5.730 5.716 5.699 5.583 5.695 . 5.651 . 5.789 5.628 5.669 5.773 CR .005 .008 .005 .007 FEZ+ .. 121 .ZOCJ .106 .145 .126 .157 .232 .106 .155 .137 nN .007 .004 HG .163 .069 .113 .126 .103 .132 .136 .132 .114 .094 Cft HA .193 .058 .210 .154 .167 .153 .113 .145 .159 .172 K 1.657 1.243 1.595 1.595 1.600 1.570 1.400 1. 597 1.558 1.697 Zit .007 .005 .014

sun 13.96:i 1l.544 13.888 13.848 13.867 13.8:iZ 13.786 13.842 13.842 13. 962

ir1rlrll SftftPL[ DIRECTORY *"'** SAMPLE HO. DESCRIPTION SflnPLE NO. DESCRIPTION ---------- ----------- ---------- -----------

11 BH L0-1 16 ABH-2 12 BH 156-5 17 ABN-4 13 ABH-1 18 ABH-12 14 ADN-2 19 ABH-13 15 ABH-2 20 RBH-16

SIOZ 45.0Z TI02 1.241 Al20l 35.86 CR20l fEO - 1.49 nKo nGO .50 CAO NA20 .66 K20 10.24 ZHO tiD

TOTAL 95.03

OXYGEH 22

SI 6.021 TI .125 AL 5.653 CR FE2+ .167 nH nG .100 CR HA .171 K 1.747 ZH

sun 1'3. 986

SftftPLE HO.

nuscount

"* RTOftIC PROPORTIOHS BASED OK SELECTED HO. Of OXYGEHS 1rlr

·"

trlr1r#r SAnPLE DIRECTORY *"lddl

DESCRIPTIOrt SftnPLE HO.

21 RBH-16

DESCRIPTIOH

BIOTITE

SI02 41.22 40.32 37 .01 36.81 35.16 35.06 35.11 33.64 34.13 33.99

TI02 .08 .06 1. 91 1.77 3.44 3.95 3.29 2.96 3.85 3.7l

AL20l 12. 98 13.12 17 .18 12. 77 18.67 19.43 19.24 19.00 19. 98 18.96 CR20l .07 .08 HO 9. 91 10.49 14.55 14.58 25.13 23.23 24.52 26.94 24.84 26.12

HHO .51 .42 .98 1.00 .35 .31 .29 .25 .23 .24 HGO 21.32 20.07 14.48 14.03 5.43 5.53 5.32 5.90 5.30 5.15 CAO Nfl20 1.02 1.08 .12 .08 .08 .11 .09 . 11 .10 K20 1.33 6.84 8.79 8.68 9.60 9.54 9.73 7.66 1.55 9.06 ZHO .13 .18

TOTAL 94.37 92.40 95.15 89.90 97.86 97 .16 97.59 96.53 96.06 97.25

** RTOnIC PROPORTIONS BASED OH SELECTED HO. OF OXYGEHS **

OXYGEH 22 22 22 22 22 22 22 22 22 22

SI 5.979 5.978 5.514 5.845 5.368 5.336 5.358 5.214 5.242 5.243 TI .009 .007 .214 .211 .395 .452 .378 .345 .445 .433 Ill 2.219 2.293 3.017 2.390 3.359 3.486 3.461 3.471 3.617 3.447 CR .009 .010 FE2t 1.202 1.301 1.813 1. 936 3.208 2.957 3.129 3.492 3.190 3.370

"" .063 .053 .124 .134 .045 .040 .037 .033 .030 .031 HG 4.609 4.435 3.215 3.320 1.235 1. 254 1. 210 1.363 1. 213 1.184 CR HA .287 .310 .035 .025 .024 .032 .027 .033 .030 K 1.356 1.294 1.671 1.759 1.870 1.853 1.894 1. 515 1.479 1. 783 ZH .014 .021

sun 15.724 15.671 15.616 15. 641 15.504 15. 411 15.494 15.475 15.255 15A92

'IWrtm SllHPLE DIRECTORY **""""

SllHPLI HO. DISCRIPTIOH SflnPLE HO. DESCRIPTION __ .. _______ ----------- ---------- -----------

1 BH UE-2 6 BHG 156-5 2 DH UE-2 7 BHG 156-5 3 BH-2 8 AG 80 195 4 BH-2 9 AG ilO 195 5 BHG 156-5 10 BHC 156-7

BIO TI Tr

SIOZ 36.11 33. 71 JJ.88 34.89 35.93 34.54 34.63 34.48 34.57 37.33 TI02 4.22 3.96 4.53 .82 .78 2.31 2.33 2.l6 1.89 1.30 AL203 20.23 18. 96 19.44 20.53 20.41 20.08 19.49 19.34 2S.09 17 .51 CR203 .07 .04 HO 20.57 25.72 24.09 19.35 19.38 20A4 21.25 2Z.59 19.85 tl.95 HHO .17 .24 .17 .34 .37 .19 .21 .39 .25 .OS HGO 5.25 5.05 5.18 8.86 9.60 8.09 8.39 7.87 6.94 15.37 CAO HR20 .04 .09 .09 .JO .lO .31 .25 .32 .25 .53 K20 9.78 8.76 9.15 9.09 9.18 8.87 8.69 8.65 7.57 8.39 ZHO .15 .17 .22 .11 .07 .08

TOTAL 96.37 96.49 96.60 94.33 96.12 95.04 95.35 96.11 96. 41 94.51 /

** ftTOnIC PROPORTIONS BASED OH SELECTED HO. or OKYG£HS **

OKYGElt 22 22 22 22 22 22 22 22 22 22

SI 5.449 5.230 5.214 5.361 5.406 5.296 5.307 5.283 5.119 5.545 TI .479 .462 .524 .095 .088 .266 .269 .272 .210 .145 Al 3.598 3.467 3.526 3.718 l.620 3.629 3.521 l.493 4.379 3.066 CR .009 .005 H2+ 2.596 3.337 3.100 2.486 2.439 2.621 2.724 2.895 2.458 1. 73l

"" .OZ2 .032 .OZ2 .044 .047 .023 .027 .051 . 031 .006 nG 1.181 1.168 1.188 2.029 2.153 1.849 1. 916 1.797 1.532 3.402 CA HA .012 .027 .027 .089 .088 .092 .074 .095 .072 .153 K 1.883 1.734 1.796 1.782 1.762 1.735 1.699 1.691 1.430 1.590 ZH .017 .019 .025 .012 .008 .009

sun 15.220 15.455 15.406 15. 621 15.621 15.537 15.550 15.589 15.232 15.648

'**"* SAHPLE DIRECTORY *"** SAnPLE HO. DISCRIPTIOH SRnPLI HO. DESCRIPTION ---------- ·---------- ---------- -----------

11 BHG 156-7 16 ABIH 12 BHG 156-7 17 ABK-4 13 BHG 151i-7 18 ABK-4 14 A8H-3 19 ABH-4 15 ABH-3 20 ABH~6

BIOTITE

SI02 38.39 37.42 37.67 36.24 37.05 36.711 36.46 311.85 35.85 35.58 TI02 1.110 1.38 1.34 .84 1.22 1.20 1.37 2.63 1.113 1.65

RL20l 11.18 17. 71 11.95 17 .67 ' 11.61 17.42 11.76 18.36 18.88 18. 79 CR203 HO 1l.47 14.16 14.22 14.67 14.18 14.62 14.93 14.26 1l.45 14.14 nHO .14 .09 .19 nGO 16.53 15.21 15.34 15.83 15.09 15.46 15.42 12.48 14.09 13.24 CAO HR20 .51 .38 .38 .40 .42 .41 .43 .39 .43 K20 7.70 7.97 7.55 7 .19 7 .77 7.67 7 .18 7.97 7.77 8.00 ZHO . 10 .15

TOTAL 94.77 9CJ6 94 .115 92.82 93.32 93.53 93.53 91. 12 91 .95 92.17

** RTOnIC PROPORTIONS BASED OH SELECTED HO. Of OXYGENS **

OXYGEN 22 22 22 22 22 22 22 22 22 22

SI 5.625 5.551 5.561 5.468 5.554 5.512 5.463 5.389 5.443 5.428 TI .154 .154 .149 .095 .138 .135 .154 .306 .163 .189 Al 2.967 3.096 3.121 3.143 3.111 J.080 3.137 3.347 3.379 J.379 CR FEZ+ 1.651 1 .-757 1.756 1.851 1. 778 1.834 1.871 1.844 1.708 1.804 nH .OHi .012 .025 nG 3.610 3.362 3.375 3.560 3.371 3A56 3.443 2.876 3.188 l.010 CR NA ... .147 .109 .111 .116 .122 .119 .129 .115 .127 K 1.439 1.508 1.422 1.384 1.486 1.468 1.373 1.572 1.505 1.557 Zit .011 .017

sun 15.457 15.575 15.494 15.613 15.554 15.608 15.560 15.482 15.514 15.536

**I'm SAnPLE DIRECTORY """""* SRftPLE HO.

.1·

DESCRIPTION SAnPlE HO. DESCRIPTION ---- ... ----- ----------- ---------- -----------

21 ABH-6 26 ABH-6 22 RBH-6 27 ABN-6 23 ABH-6 28 RBH-9 24 RBH-6 29 RBH-9 25 RDH-6 30 RBH-9

BIO TI TE

SI02 J5.39 35.11 J5.80 36.86 35.49 35.02 J7 .11 J6.19 34.57 33.96 TI02 2.94 3.55 3.82 3.18 2.81 2.13 3.01 3.27 3.45 J.42 RL20l 18.24 19.51 19.18 19.85 19.28 19.85 20.64 19.09 19.73 19.28 CR20l ... FEO 14.64 21.39 20.'53 20.36 19.61 19.19 18.57 18.59 23.19 21.96 nHO .20 .35 . 31 .29 .26 .n .JO .26 .19 .22 HGO 11. 81 8.53 8.05 8.85 9.81 9.77 6.66 7 .18 6.71 6.57 CAO .21 Hlt20 .36 .34 .27 .30 .31 .35 .29 .16 .21 .25 K20 8.06 9.07 8.94 9.04 8.95 8.83 7 .81 7.63 8.50 8.46 ZHO .07 .09 .12 .10 .28 .27

TOTAL 91.64 97.92 96.99 98.85 96.8l 95.65 94.39 92.37 96.55 94.39

1r1r ftTOnIC PROPORTIOKS BASED OH SELECTED HO. OF OXYGEHS iric

OXYGEH zz Zl Z2 Z2 22 22 Z2 22 22 22

SI 5.446 5.250 5.J68 5.399 5.317 5.302 5.584 5.586 5.267 5.286 TI .340 .399 .431 .350 .317 .243 .341 .380 .395 .400 Al 3.309 3.439 3.390 3.427 3.405 3.542 3.661 3.473 3.543 J.537 CR FE2+ 1.884 2.~75 2.575 2.494 2.457 2.430 2.337 2.400 2.955 2.859 Hit .026 .044 .039 .036 .033 .029 .038 .034 .025 .029 HG 2.709 1. 901 1.799 1. 932 2.190 2.204 1.493 1.652 1.524 1. 524 CR .034 HA .107 .099 .079 .085 .090 .103 .085 .048 .062 .075 K 1.582 1.730 1. 710 1.689 1. 711 1.705 1.499 1.502 1.652 1.680 ZH .008 .010 .013 .011 .031 .031

sun 15.404 15.546 15.400 15. 425 15.564 15.589 15.037 15. 074 15.423 15. 422

trtdrlr SRnPLE DIRECTORY 1rlr1rlr

SftftPLE HO. DESCRIPTIOH SAftPLE lfO. DESCRIPTiotl ________ .. _ ________ .. __ --------- -----------

31 RSH-9 36 RBH-10 12 RBH-10 37 ftBH-13 33 ABH-10 38 RBH-13 34 ABH-10 39 RBH-16 35 RSH-10 40 RBH-16

BIOTITE

SI02 33.99 J4.04 J4.08 35.60 JS.68 35.66 J4.77 35.lS 33.97 37.64

TI02 l.53 3.25 2.98 1.83 1.06 1.J9 1.83 2.41 3.44 5.11

fll203 19.22 19.18 19.19 19 .64 19. 95 19.85 19.45 19.73 16.61 15.74

CR20l HO 22.43 23.05 23.41 16.0l 16.37 16. 91 17 .08 17.83 11.0l 9. 91

nHO .27 .25 .22 .12 .13 .15 .15 .09 .10 .27 nGo 6.81 6.79 6.99 12.62 13.19 12.51 12.02 10.23 18.84 17.06 CftO HR20 .22 .20 ,.21 .28 .30 .41 ... 29 .33 .32 .22 K20 8.68 8.61 8.40 8.02 8.26 8.32 8.38 8.23 6.55 9.43 ZHO .35 .12 .47 .36

TOTAL 95.50 95.49 95.48 94.14 94.94 95.20 93.97 94.20 91.53 95.74

1dr ATOftIC PROPORTIONS BASED OH SELECTED KO. OF OXYGENS *"

OXYGElt 22 22 22 22 22 22 22 22 22 22

SI 5.251 5.264 5.268 5.350 5.331 5.332 5.289 5.363 5.159 5.476 TI .410 .378 .346 .207 .119 .156 .209 .275 .393 .559 ftL 3.500 3.4% 3.497 3.479 l.513 3.499 3.487 l.52S 2.973 2.699 CR fE2+ 2.898 2. 981 3.027 2.015 2.046 2 .115 2.173 2.262 1.401 1.206

"" .035 .033 .029 .015 .016 .019 .019 .012 .039 .033 ttG 1.568 1.565 1.610 2.827 2.937 2.788 2.725 2.313 4.264 3.699 Cft Hft .066 .060 .063 .082 .087 .119 .086 .097 .094 .062 K 1. 711 1.699 1.657 1.538 1.575 1.587 1.626 1.593 1.269 1.750 ZH .040 .014 .053 .039

sun 15.478 15.489 15.497 15.513 15.624 15. 615 15.614 15.443 15.644 15.522

fdrfdr SAnPLE DIRECTORY l!Wtfdr

SftftPLE HO. DESCRIPTION SftnPLE HO. DESCRIPTIOH

---------- ----------- ---------- ----------· 41 RBH-16 -46 SK-3 42 ftBH-16 47 SK-3 43 RBH-16 48 SK-4 44 SK-3 49 JE-2 45 SK-3 50 JE-i

BIOTIT£

5102 38.38 38.05 38.40 37.98 35.73 35.25 34.48 35.37 36.57 35.36 TI02 5.16 5.17 5.00 5.01 3.05 l.93 l.40 4.14 1.30 4.03 AL203 16.19 15. 99 15.81 15. 95 17 .34 17.62 18.57 17.83 18.02 16. 96 CR20l ... 07 HO 9.44 9.76 9.45 9.76 13.48 15.96 13.29 11.59 10.19 15.24 nHO .21 .23 .2l .26 .08 .09 .19 .20 .10 .14 nso 17 .87 17.26 17. 93 17 .16 14.78 12.56 13.97 14.01 18. 35 13.32 CAO .33 HA20 .16 .19 .23 .21 .14 .08 .08 .08 .15 .09 K20 8.92 9.55 9.56 9.69 9.08 9.39 9.49 9.57 9.05 9.37 ZHO .27 .34 .33 .34

TOTAL 96.60 96.54 97.Z7 96.36 93.75 94.88 9JA7 94.79 93.73 94.51

** ATOnIC PROPORTIONS BASED OH SELECTED NO. OF OXYGENS **

OKYGEH 22 22 22 22 22 22 22 22 22 22

SI 5.487 5.480 5.485 5.487 5.381 5.3ZO 5.227 5.290 5.406 5.345 TI .555 .560 .537 .544 .345 .446 .388 .466 .145 .458 lll 2.728 2.714 2.662 2.716 l.078 l.134 3.318 l.143 3.140 3.022 CR .008 FEZ+ 1.129 1.176 1.129 1.179 1.698 2.014 1.685 1.700 1.260 1.927 nH .025 .029 .028 .032 .010 .012 .024 .025 .013 .01S ftG 3.807 3.705 l.817 3.694 3.317 2.825 3.156 3.123 4.043 3.001 CA .051 HA .044 .053 .064 .059 .041 .023 .024 .023 .043 .026 K 1.627 1.755 1.742 1.786 1.745 1.808 1.835 1.826 1.707 1.807 ZH .029 .036 .035 .036

sun 15.430 15:507 15.550 15.533 15.623 15.583 15.656 15.597 15. 755 15.603

*1rlt'fr SAnPL£ DIRECTORY *>Wn'r

SAnPL£ HO. _,DISCRIPTIOH SftftPLE HO. DESCRIPTION ---------- ----------- ----------

___ .. _______

51 JE-2 56 JE-29 52 J[-2 57 JE-29 53 JE-2 58 JE-29 54 J[-.2 59 JE-29 55 JE-29 60 JI-29

BIOTITE

SI02 36.62 36.34 36.86 35.59 36.11 36.26 38.26 38.21 Tl02 3.02 3.10 3.30 3.33 3.27 3.16 .49 .99 AL20l 16.58 16.38 16.61 15.98 16.29 16.31 16.79 15.51 CR20l .06 .05 HO 12.44 12. 97 11.42 13.98 1l.40 12. 98 4.98 6.64 HHO .10 .1l .31 HGO 15.65 15.47 16.46 15.37 15.65 15.74 21.11 21.48 CAO HA20 .21 .21 .24 .2l .23 .25 .36 .35 K20 9.40 9.25 9.60 9.06 9.l2 9.39 S.68 8. 51 ztto .52 .16

TOTAL 93.98 93.72 94.54 93.64 94.27 94.09 91.32 92.16

** ATOHIC PROPORTIONS BASED OH SELECTED HO. OF OXYGENS **

OXYGEH 22 22 22 22 22 22 22 22

SI 5.477 5.464 5.459 5.395 5.418 5.439 5.651 5.640 TI .340 .151 .368 .380 .169 .l57 .054 .110 AL 2.923 2.901 2.900 2.855 2.881 2.884 2.923 2.698 CR .007 .006 FEZ+ 1.556 1.611 1.414 1.772 1.681 1.628 .615 .szo HK .01l .016 .·039 HG 3.488 l.467 l.633 l.472 l.499 l.519 4.647 4.72.5 CA HA .061 .061 .069 .068 .067 .073 .103 .100 K 1.794 1. 774 1.814 1.752 1.784 1.797 1.636 1.603 ZH .057 .017

sun 15.646 15. 651 15.662 15.707 15.699 15.697 15.702 15.752

trlr1rtt SftftPLE DrnECTORY trlr1rlr

SAHPLE HO. DESCRIPTIOH SAftPLE HO. DESCRIPTIOH ---------- ----------- ---------- ---·--------

61 J[-31 66 JE-32 62 JE-31 67 JE-74 63 J[-31 68 JE-74 64 JE-32 65 J[-32

CHLORITE

SI02 29.68 31.86 29.7J J1.09 J1.67 33.28 30.J7 J0.20 25.10 23.45 TI02 HD .07 HD .11 HD .05 AL20l 9.95 8.42 10.32 21.25 21.05 21 .64 21.02 20.53 22.29 22.21 CR20l rEO 43.66 43.47 44.27 7.93 6.41 6.08 5.94 8.85 25.59 26.85 nHO 2.02 2.08 2.03 1.52 1.55 1.52 1.78 1.74 1.81 2.28 nGO 2.41 1.80 2.22 24.10 25.20 22.95 26.22 24.15 11. 31 9.79 CAO .14 .24 .06 .06 .06 .08 .06 HD HD HD HA20 .20 .14 .06 .04 .02 .02 .04 .04 K20 .32 .39 .25 .05 .11 .52 .05 .09 .34 ZHO ·.15 .74 .84 .76 .83 .87 1.25 l.7J

TOTAL 88.38 88.55 88.94 86.77 87.00 86.87 86.38 86.51 87.80 88.38

tm RTOttIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGENS fl~

OXYGEN 28 28 28 28 28 28 ZS 28 28 28

SI 6.965 7.424 6.935 6.034 6.087 6.364 5.892 5.940 5.378 5.131 TI .010 .016 .008 Al 2.752 2.313 2.837 4.861 4.769 4.878 4.807 4.759 5.630 5.728 CR H2+ 8.569 8.472 8.636 1.287 1.030 .972 .964 1.456 4.586 4.913 nH .402 . 411 .401 .250 .252 .246 .293 .290 .329 .423 ftG .843 .625 .772 6. 971 7.218 6.540 7 .581 7.079 l.612 3.192 CR .035 .060 .015 .012 .012 .016 .012 HR .091 .063 .027 .015 .007 .008 .017 .017 K .096 ;116 .074 .012 .027 .127 .012 .023 .093 ZH .026 .106 .119 .107 .119 .126 .198 .603

sun 19. 752 19.509 19.697 19.538 19.540 19. 261 19.695 19. 691 19.854 20.014

. 1nWrti SAnPLE DIRECTORY fr"'**

SRnPLE HO. DESCRIPTION SAnPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

1 BH ME-2 6 JE-7 2 BH UE-2 7 JE-7 l DH NE-2 8 JE-7 4 J£-7 9 JE-i4 5 JE-7 10 JE-H

CHLORITE

SI02 23.93 23. 71 26.33 28.78 26.40 26.17 30.12 26.26 25.42 27.92

TI02 HD HD . 10 :26 . .27 .15 2. 51

AL20l 21 .05 21.29 19.93 18. 93 19.80 19.61 19.76 20.10 18. 71 19.82 CR203 FEO 21.18 27.80 20.19 19.83 19.92 19.33 16.89 19.10 18.73 16.56 HHO 2.00 2.10 2.23 2.11 2.30 2.29 1. 97 2.09 2.1 q 1.95 HGO 11.Tl 11.47 11.44 19.37 18.15 17.28 15.68 16.56 16.26 16.12 CAO .04 .04 HD .10 .04 HD .09 HR20 .02 .06 .03 .OJ .08 .02 .04 K20 .04 .04 HD .06 ZltO 1.40 1.41 1.41 1.65 1.48 3.26 l.87 2.81 :L64 5.25

TOTAL 87.35 87.86 87.72 90.77 88.09 88.23 88.63 87 .19 87.48 87 .01

** ATOftIC PROPORTIOHS BASED OH SELECTED HO. or OXYGEHS **

OXYGEtt 28 28 28 28 28 28 28 28 28 28

SI 5.231 5.174 5.504 5.773 5.492 5.481 6.126 5.533 5.386 5.814 TI .016 .041 .041 .024 .400 AL 5.424 5.476 4. 911 4.476 4.855 4 .841 4.737 4.992 4.673 4.865 CR ._

FE2+ 4.969 5.073 3.530 3.327 3.466 3.386 2.873 3.366 3.319 2.884 HK .370 .388 .395 .358 .405 .406 .339 .373 .384 .344 HG l.821 l.730 5.433 5.790 5.627 5.393 4.753 5.200 5.134 5.003 CR .009 .009 .021 .009 .020 HA .008 .024 .012 .012 .033 .008 .016 K .010 .011 .016 ZH .226 .227 .218 .244 .227 .504 .581 .437 .570 .807

sun 20. 0:>4 20.089 20.037 19. 989 20.081 20.064 19.475 19. 96'9 19.886 19. 769

~ SAHPLE DIRECTORY -SAHPLE HO. DESCRIPTION SAftPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

11 JE-14 16 JE-18 . 12 J[-14 17 JE-i8

1l JE-16 18 JE-18 14 J[-16 19 JE-i8 15 JE-16 20 JE-18

...

CHLORITE

SI02 27.97 25.79 26.21 25.56 29.00 29.21 25.3'1 25.65 25. 91 26.01 TI02 .05 .0'1 HD .06 tiD HD AL203 21.72 20.59 22.85 21.39 21.74 20.55 21.88 20.62 20.09 21.02 CR20l f [0 17.90 19.86 23.77 24.9l 21.55 22.78 25.38 21.66 21.41 21.82 nHO 2.13 2.21 1.83 1.95 1.46 1.48 1.83 2. 51 2.40 2.55 nGO 13. 91 14.01 11.46 11.31 12.08 11.65 12.16 14. 7l 15.'05 14.67 CAO .08 .06 .15 .12 .16 .15 .06 .04 .06 .04 NA20 .06 .05 .13 .06 .05 .06 .02 .04 K20 .04 HD .13 .09 .13 .21 .07 ND ZHO 2.55 2.58 1.74 1.78 2.61 2. 71 1.78 2.56 2.65 2.58

TOTAL 86.36 85.23 88.27 87 .19 88.82 88.83 88.56 87 .79 87.66 88.71

** ftTOnIC PROPORTIONS BASED Off SELECTED HO. or OXYGENS **

OXYGEN 28 28 28 28 28 28 28 28 28 28

SI 5.849 5.578 5.519 5.511 5. 971 6.066 5.384 5.445 5.504 5.456 TI .008 .006 .010 AL 5.354 5.249 5.671 5.436 5.276 5.031 5.480 5.159 5.030 5.199 CR H2+ 3.130 3.592 4.186 4.496 3.711 3.957 4.510 3.845 l.803 3.829

"" .377 .405 .326 .356 .255 .260 .329 .451 .432 .453 nc 4.335 4.516 3.596 3.635 3.707 3.606 3.851 4.660 4.764 4.588 CA .OH1 .014 .Ol4 .028 .Ol5 .033 .014 .009 .OH .009 HA .024 .021 .053 .025 .020 .024 .008 .016 K .011 .035 .025 .034 .056 .019 ZH .394 .412 .271 .283 .397 .416 .279 .401 .416 .400

sun 19.492 19.804 19.690 19. 795 19.412 19.453 19.876 19. 980 19.990 19. 939

**** SftHPLE DIRECTORY **** SftnPLE HO. DISCRIPTIOH SftnPLE NO. DESCRIPTION ---------- ----------- ---------- -----------

21 JI-18 26 JI-19 22 J[-18 27 JE-i9 23 JI-19 28 JI-20 24 J[-19 29 JE-20 25 J[-19 JO J[-20

CHLORITE

5102 tl.08 Z7.23 27.84 27.23 27.64 27.49 27.30 27 .34 27.26

TI02 .04 HD. ltD HD .04 HD HD RL20l 19.26 19.15 19.7l 19.15 19.29 19.29 18.93 19.14 19.23 CR20J FEO 10. 93 10.70 10.53 10.70 9.08 10.08 11. 81 9.04 10.03

HHO l.29 3.00 3.58 l.08 3.76 3.43 2.77 3.81 3.38 HGO 21.82 22.22 21.90 22.22 21.98 22.10 21.57 21.68 21.82 Cl\O .06 HD HD HD .06 HD HD .08 .05

IUl20 .06 .06 .02 .05 .06 .03 .06 .04 .03 K20 HD HD HD HD HD ZHO 4.72 4.60 5.34 4.60 5 .. 67. 5.12 4.0J 5.n 4.88

TOTAL 87.26 87 .10 89.02 87.11 87.54 87.64 86.54 86.89 86.70

""' ATOHIC PROPORTIONS BASED OH SELECTED HO. OF OXYGEHS **

OXYGEH 28 28 Z8 28 Z8 28 28 28 28

SI 5.562 5.585 5.604 5.585 5.640 5.607 5.639 5.628 5.613 TI .006 .006 AL 4.663 4.629 4.681 4.629 4.639 4.638 4.609 4.644 4.667 CR FEZ+ 1.877 1.835 1.7TJ 1.835 1.549 1. 719 2.040 1.556 1.727 HH .572 .535 .610 .535 .650 .593 .495 .6M .589 HG 6.679 6.792 6.570 6.792 6.684 6.718 6.640 6.651 6.696 CR .013 .013 .018 .011 HA .024 .024 .008 .020 .024 .012 .024 .016 .012 K ZH .716 .697 .794 .697 .854 . 771 .615 .871 .742

sun Z0.·113 20.108 20.057 20.109 20.053 20.078 20.068 20.053 20.062

ttfr1r SRHPLE DIRECTORY *"'**

SAHPLE HO. DISCRIPTIOH SAHPLE HO. DESCRIPTIOH

---------- ----------- --·------- -----------36 JE-36

l2 JE-36 37 JE-36 3l JE-36 la JE-36 l4 J[-36 39 JE-36 15 JE-36 40 JI-36

CHLORIT£

SI02 27.79 27.35 25.12 Z5.18 25. 10 23.2S 26.14 TI02 HD 2.42 AL20J 19.51 19.09 21.45 20.49 21.34 21.58 18.43 CR20l HO 9.85 9.43 2l.95 24.44 24.22 28.JJ 20.61 HHO 3.48 l.68 ,1.66 1.78 1.75 1. 75 1.41 nGO 22.19 21.98 12.48 13.19 14.04 10.74 15.82 CAO .05 .06 .04 ND .05 ... 06 ltl\20 .OJ .04 ·.06 .04 K20 HD HD HD .09 ZHO 5.39 5.39 1.18 1.50 .81 .81 .97

TOTAL SS.34 87.02 85.97 86.65 S7.26 86.57 S5.95

** ATOnIC PROPORTIONS BflSED OH SELECTED HO. or OKYGEHS *"'

OXYGEM 28 28 ZS ZS ZS 28 28

SI 5.620 5.619 5.444 5.450 5.357 5.150 5.572 TI .388 AL 4.651 4.623 5.480 5.227 5.368 5.627 4.631 CR FI2+ 1.666 1.620 4.341 4.424 4.323 5.242 J.674 HH .596 .640 .305 .326 .316 .328 .255 HG 6.688 6.729 4.031 4.254 4.466 l.541 5.026 CA .011 .013 .009 .012 .014 lift .012 .016 .025 .017 K .024 ZH .805 .818 .189 .240 .128 .1J2 .153

sun 20.058 20.078 19.833 19.945 19. 959 20.040 19.737

"'"'** SAftPLE DIRECTORY ****

SAftPL£ HO. DESCRIPTIOH SftftPLI HO. DESCRIPTION ---------- ----------- ---------- ·----------

41 J(-36 '46 OF-7 42 JE-36 47 OF-7 43 Of-7 44 or-1 45 Of-7

~ I

GllRHET

5102 36.72 36.60 36.73 36.50 36.45 36.97 36.97 36.43 36.03 36.21 HD HD

TI02 RL203 21.02 21.00 20.80 20.58 20.70 20.99 20.86 21 .47 21.60 21.49

HD ND CR20l HO 21.05 22.14 22.11 21.28 20.53 21.86 22.04 25.32 .24.79 25.13

HMO 18.95 16. 92 17 .51 18.07 19.50 17 .66 17.50 15. 99 16.50 15.32

HGO 1.32 1.52 1.SO 1.46 1.ll 1.52 1.52 .96 .92 1.02

CflO .86 1.86 1.59 1.42 .88 1.57 1.44 .57 .60 .63 .02

Kfl20 K20

TOTAL 99.92 100.04 100.211 99.31 99.37 100.57 100. 33 100.76 100.119 100.35

"* ATOHIC PROPORTIONS BllS£D OH S£LECT£D NO. Of OXYGENS 111r

OXYG£M 12 1l 12 12 12 12 12 12 12 12

SI 2.995 2.979 2.988 2.996 2.994 2.993 3.000 2.962 2.940 2.954

TI RL 2.020 2.015 1.995 1. 991 2.004 2.003 1.995 2.057 2.078 2.066

CR f [2+ 1.436 1.507 1.504 1. 461 1.410 1.480 1.496 1.n.2 1.692 1. 715

Ht! 1.309 1.167 1.207 1.256 1.357 1.211 1.203 1.101 1.1111 1.093

HG .160 .184 .182 .179 .160 .183 .184 .116 .112 .124

CA .075 .162 .139 .125 .077 .136 .125 .050 .052 .055

HA .003

K

sun 7.995 a.off' 8.014 8.008 8.0011 8.006 8.003 8.009 8.020 8.011

~ SftHPLE DIRECTORY *"'*"'

SRHPLE HO. DESCRIPTION SAHPLE HO. DESCRIPTION

---------- --------------------- -----------1 BH llE-1 6 BH llE-1

2 BH llE-1 CORI· 7 BH UI-1

3 BH llE-1 RIH 8 BH L0-1 CORE

4 BH llE-1 CORE 9 DH L0-1 RIH

5 DH llE-1 RIH 10 BH L0-1 CORE

...

GRRH£T

SI02 36.15 36.15 36.41 36.33 37.25 37.29 37.49 37.56 37.27 36.99 TI02 .09 ND HD RL20J 21.40 21.52 21.57 21.53 21. 61 21.89 22.01 21.92 21.12 21.08 CR20l HD FEO 25.13 23.83 24.60 25.07 35.95 35.33 34.73 35.34 34. 71 34.92 nNO 15.93 17.59 16.33 15. 91 1.25 1.21 1.24 1.29 5.80 5.72 nso .93 .81 1.04 1.06 5.18 5.29 5.42 5.45 1.42 1.38 CAO .57 .29 .59 .59 .33 .34 .35 .30 1. 95 1.93 HR20 .03 .03 .02 K20

TOTAL 100.11 100.33 100.60 100.52 101 .57 101.35 101.26 101.86 102.27 102.02

** ATOftIC PROPORTIOHS BASED OH SELECTED HO. Of OXYGEHS --

OXYGEH 12 12 12 12 12 12 12 12 12 12

SI 2.958 2.953 2.960 2.957 2.943 2.942 2.951 2.947 2.981 2.971 TI .006 AL 2.064 2.072 2.067 2.066 2.012 2.036 2.042 2.027 1. 991 1. 995 CR FI2+ 1.720 1.628 1.672 1. 707 2.375 2.331 2.286 2.319 2.322 2.345 ttH 1.104 1.217 1.124 1.097 .084 .081 .083 .086 .393 .389 nG .113 .099 .126 .129 .610 .622 .636 .637 .169 .165 CR .050 .025 .051 .051 .ozs .029 .030 .025 .167 .166 KR .005 .005 .OOJ K

sun 8.010 8.007 8.007 8.008 8.051 8.040 8.030 8.040 8.023 8.032

1rlr1t1r SftftPLE DIRECTORY· *"*"'

SRftPLE HO. DESCRIPTIOH SftftPL! HO. DESCRIPTION ---------- ----------- ---------- -----------

11 Bd L0-1 Ritt 16 240 AG 56 RIH 12 BH L0-1 17 240 AG 56 COR£ 13 BH L0-1 18 240 AG 56 RIH 14 DH L0-1 19 AG 80 195 15 240 AG 56 CORE 20 AG 80 195

.t·

GRRHET

SI02 l7.32 36.99 l6.89 l7 .16 36.74 l7 .10 36.91 36.79 l7.09 36.39

TI02 ~D .06 .04

RL20l 21.28 21-. 08 21.28 21.25 21.12 21.28 21.11 21.15 21.26 21. 31

CR203 HD FEO 34.96 32.19 ll.09 32.84 33.05 33.08 33.01 32.84 33.04 29.45

nHO J.67 8.71 8.82 8.78 8.88 8.67 8.80 8.66 8.76 10.22

nGO 1.29 1.40 1.35 1.53 1.32 1.48 1.27 1.45 1.37 1.88

CllO 1.90 1.16 1.16 1.21 1.10 1.19 1.77 1.11 1.28 1.76

HR20 K20

TOTAL 102.42 101.53 102.61 102.77 102.21 102.80 102.93 102.00 102.80 101.07

.*'J' ATOnIC PROPORTIOHS BAStD OH StLECTED HO. OF OKYGEHS "*

OXYGEH 12 12 12 12 12 12 12 12 12 12

SI 2.980 2.981 Z.954 2.965 2.956 2.962 2. 951 2.960 2.963 2.940 TI .004 .002 AL 2.003 2.003 2.009 1.999 2.003 2.002 1.989 2.006 2.002 2.030 CR FE2+ 2.335 2.170 2.216 2.192 2.224 2.209 2.207 2.210 2.207 1. 990

"" .384 .595 .598 .594 .605 .586 .596 .590 .593 .699 nG .15'1 .168 .161 .182 .158 .176 .151 .174 .163 .226 CR .163 .100 .100 .103 .095 .102 .152 .096 .110 .152 HA K

sun 8.018 8.017 8.040 8.035 8.042 8.017 8.051 8.0l7 8.037 8.042

fttrtrlr SAnPLE DIRECTORY **"* SAnPLE HO. DESCRIPTION SAnPLE HO. DESCRIPTIOH ---------- ----------- ---------- -----------

21 A~ 80 195 26 BHG 156-7 CORE 22 BHG 156-7 CORE 27 BHG 156-7 RIH 23 BHG 156-7 RIH 28 BHG 156-7 CORE 24 DHG 156-7 CORE 29 BHG 156-7 RIH 25 DHG 156-7 Rin 30 RBH-4 CORE

GllRHET

Sl02 36.41 36.40 37.02 35.54 36.22 36.34 34.75 36.10 36.21 36.21 TI02 HD flL20J 21.90 21.31 21.64 21 •. 69 21.80 21 .25 21.09 21.72 21.37 21.23 CR20l HD .05 .04 HD HO 32.95 32.91 29.47 29.31 29.54 29.89 29.68 32.42 29.87 31 .49 ft HO 10.98 6.15 10.27 10.01 9.80 9.34 11.11 6.51 10. 72 7 .10 ft GO 1.58 2.64 1.78 1.89 1.80 2.11 1.59 2.71 1.57 2.45 CflO .77 1.52 1.55 .7J 1.58 1.58 .93 1.54 .93 1.61 HA20 K20 -

i

TOTAL 104.61 100. 93 101.78 99.17 100.74 100.51 99.15 101. 02 100.71 100.13

fl~ ftTOnIC PROPORTIONS BftS[D OH SELECTED HO. or OX~GEHS ~

OXYGEH 12 12 12 12 12 12 12 12 12 12

SI 2.882 2.936 2.961 2.921 2.930 2.947 2.888 2.909 2.943 2.941 TI fll 2.043 2.026 2.040 2 .101 2.078 2.031 2.066 2.063 2.047 2.033 CR .003 .003 HZ+ 2.181 2.220 1. 971 2.014 1. 998 2.027 2.063 2.185 2.030 2.139

"" .736 .420 .696 .697 .671 .641 .782 .446 .738 .489 ftG .186 .317 .212 .231 .217 .255 .197 .325 .190 .297 Cfl .065 .131 .133 .064 .137 .137 .083 .133 .081 .140

"" K

sun 8.096 8.051 8.017 8.029 8.031 8.038 8.079 8.060 8.032 8.041

iWl1Wr SftftPLE DIRECTORY tt1rll

SAnPLE KO. DESCRIPTION SRftPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

l1 ftSH-4 RIH 36 ftBH-4 CORE 12 ABlt-4 CORE 37 ABH-4 RIH 33 ASH-4 RIH 38 ABH-4 CORE 34 flBH-4 COR[ 39 ABH-4 RIH l5. ABH-4 RIH 40 ABH-4 CORE

...

GARNET

' 37.74 l7.44 37.5l 37.34 35.86 36.45 5102 35.86 l5.94 34.85 37.l6 TIOZ HD HD

ftLZOl 21.55 21.21 20.96 21.51 21.79 21.75 21.31 20.61 21 .45 21.68

CR203 ND HD FEO 29.82 29.81 29.50 30.4l 11.84 31.74 12.44 31.96 3'3.l5 12.17

""° 10.81 8.70 10.51 l.1q 1.97 2.00 1.96 1.93 1.98 1.70

ttGO 1.71 2.1Q 1.75 6.05 6.04 5.83 5.52 5.91 5.16 6.37

CAO 1.00 1.70 f.51 1.94 1.68 1.69 1.6l 1.69 1.59 1.6l

"HA20 K20

TOTAL . 100.78 99.52 99.10 100.45 101.06 100.47 100.39 99.48 99.39 100.00

** ATOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGENS 111c

OXYGEH lZ 12 12 12 12 12 12 12 12 12

SI 2.916 2.940 2.893 2.950 2.958 2.954 2.973 2.984 2.896 2.900

TI AL 2.065 2.047 2.051 2.004 2.01l 2.02l 1.990 1. 94J 2.042 2.0JJ

CR f [2+ 2.028 2.041 2.048 2.009 2.087 2.094 2.149 2.136 2.252 2.141 HH .745 .603 .739 .210 .131 .1J4 .132 .131 .135 .115 HG .207 .256 .216 .712 .706 .685 .652 .704 .621 .755 Cft .087 .149 .136 .164 .141 .143 .138 .145 .138 .139 Hft K

sun 8.050 8.036 8.082 8.049 8.036 8.034 8.0l3 8.0113 8.084 8.083

~ SftftPLE DIRECTORY *"'**

SftftPLE HO. DESCRIPTION SftftPLE HO. DESCRIPTIOH ... -------- ---------- ---------- -----------

41 ABH-4 Ritt .46. ABH-6 42 ABH-4 CORE 47 ABH-6 43 ABH-4 RIH 48 ABH-6 44 ABH-6 49 ftBH-6 45 ftBH-6 50 ftBH-6

GARNET

SI02 J7.08 J6.88 J9.47 J9.04 J9.25 l9.1Z J8.87 J8.75 JB.76 38.81 TI02 HD .04 HD HD HD HD .04 .04 .04 fll203 20.99 21.64 22.09 22.14 22.0l 22.06 22.22 22.29 22.16 22.13 CR20l HD HD TEO 32.86 31.51 18.10 19.41 18.01 18.12 18.38 18.11 11. 98 18.61 ttHO 2.17 1. 97 9.50 9.49 9.71 9.64 9.50 9.85 9.77 10.0J nGO 5.07 6.43 9.21 8.61 9.28 9.34 9.11 9.11 9.11 8.65 CAO 1.69 1.78 2.10 2.09 2.17 2.13 2.38 2.39 2.42 VIJ HA20 .03 .02 .02 K20

TOTAL 99.90 100.21 100.51 100.81 100.49 100.44 100.52 100.56 100.26 100. 70

*" ATOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEHS *"

OXYGEN 12 12 12 12 12 12 12 12 12 12

SI 2.966 2. 921 3.013 2. 991 3.001 2.994 2.978 2.969 2.977 2.978 TI .002 .002 .002 .002 AL 1.979 2.020 1. 987 2.000 1.985 1. 990 2.006 2.013 2.006 2.002 CR TI2+ 2.198 2.087 1.155 1. 244 1.152 1.160 1.178 1.160 1.155 1.194 HH .147 .132 .614 .616 .629 .625 .616 .639 .636 .652

"' .604 .759 1.048 .983 1.057 1.065 1.040 1.040 1.043 .989 CR .145 .151 .172 .172 .178 .175 .195 .196 .199 .200. HA .004 .OOJ .003 K

SUH 8.042 8:069 7 .991 8.007 8.005 8.010 8.0ZO 8.024 8.0ZO 8.018

~ SAftPLI DIRECTORY trlrtr1t

SftftPLE HO. DISCRIPTIOH SAftPLE HO. DESCRIPTIOH ---------- -----------

_____ ., ____ -----------

51 ABH-6 56 JE-2 52 ABH-6 57 JE-J 53 J[-2 58 JE-3 54 JE-2 59 J[-3 55 J£-2 60 JE-3

GftRHET

SI02 38.46 38.19 37.37 37.74 36.56 36.89 36.96 37 .01 37.30 37 .14 TI02 .04 KD HD. MD .08 .05 .07 .09 .13 .14 ftl20l 21.86 21.69 20.94 21.22 21.46 21.20 21.44 21.53 21.20 20.82 CR20l .04 KD HD FEO 19.99 20.05 19.41 20.68 11.21 16.79 11.18 17 .26 8.72 8A6 HHO 10.80 10.67 13.55 14.13 18.74 18.94 18.72 18.78 22.80 23.26 HGO 1.29 7.27 5.58 4.55 toz 3.05 2.95 3.18 4.00 4.00 CAO 2.14 1.87 1.89 1.97 3.78 3.75 . 3.71 l.80 4.98 4.97 Hft20 .02 .02 K20

TOTAL 100.60 99.76 98.80 100.35 . · 100.85 . 100~67 101.03 101.65 99.15 9'8.81

""" ATOHIC PROPORTIONS BASED OM SELECTED NO. OF OXYGENS *""

OXYGEN 12 12 12 12 12 12 12 12 12 12

SI Z.984 2.987 2.992 2.995 2.925 2.951 2.946 2.934 2.980 Z.983 TI .002 .005 .003 .004 .005 .008 .008 ftL 1.999 2.000 1. 976 1.985 2.024 1.999 2.015 2.012 1.996 1. 971 CR .003 HZ+ 1.297 1.312 1.300 1.372 1.151 1.123 1.145 1.144 .583 .568 ttH .710 .707 .919 .950 1.270 1.284 1.264 1.261 1.543 1.583 HG .843 .848 .666 .538 .360 .364 .JSO .376 .476 .479 CA .178 .157 .162 .167 .124 . 321 .317 .323 .426 .42B HA .003 .003 K

sun 8.016 8.011 8.018 8.010 8.059 8.046 8.042 8.055 8.013 8.024

"lltrfrlt SftftPLE DIRECTORY frhtrlr

SftHPLE HO. DESCRIPTION SftHPU HO. DESCRIPTIOH ---------- ----------- ---------- -----------

61 JE-l 66 JE-iO 62 JE-J 67 JE-10 6l JE-7 68 JE-iO 64 JE-7 69 JE-H 65 JE-10 70 JE-i4

GARHIT

SIOZ 37.'/.7 39.15 37.14 37.1.7 39.15 38.96 38.47 37.75 38.95 39.00 TI02 .14 .13 .14 .14 .06 HD .04 .06 .05 .07 Al20l 21.06 21.20 20.82 21.06 22.78 22.77 22.23 22.07 21. 91 22.02 CR20J HD IW FEO 8.60 8.72 8.46 8.60 15.95 15. 97 15.56 15.42 12.69 12.62 nKO 22.75 22.80 2l.26 22.75 10.85 10.M 11. 92 12.77 1S.22 15.67 ft GO 4.23 4.01 4.00 4.23 9.79 9.68 9.21 8.62 8.96 8.87 CftO 4.99 4.98 4.97 4.99 2.16 2.18 2.20 2.25 2.09 2.16 KA20 .02 K20

TOTAL 99.04 101. 01 98.81 99.04 100.74 100.42 99.63 98.94 99.89 100. 41

"'* ATOnic PROPORTIOHS BASED OK SELECTED HO. OF OKYGEHS "'*

OKYGEH 12 12 12 12 12 12 12 12 12 12

SI 2.980 3.052 2.983 2.980 2.972 2.968 2.969 Z.950 2.999 2.992 TI .008 .008 .008 .008 .003 .002 .004 .003 .004 Al 1.985 1. 948 1. 971 1.985 2.038 2.045 2.022 2.033 1. 989 1. 991 CR FE2+ .575 .569 .568 .575 1.012 1. 018 1.004 1.008 .817 .810 HH 1.541 1.506 1.583 1.541 .698 .700 .779 .845 .993 1.018 HG .504 .466 .479 .504 1.107 1.099 1.059 1.004 1.028 1.014 CA .427 .416 .428 .427 .176 .178 .182 .188 .172 .178 HA .003 K

sun 8.020 7.965 8.024 8.020 8.006 8.008 8.018 8.031 8.003 8.008

~ SAnPLE DIRECTORY 'lt1dWr

SAnPLE HO. DESCRIPTIOH SAnPLE HO. DESCRIPTIOH ---------- -·---------

_________ .. -----------

71 JE-14 76 JE-i8 72 JE-18 77 JE-19 73 JE-18 78 JE-i9 74 JE-18 79 JE-20 75 JE-18 80 JE-zO

...

GARHET

SI02 38.78 38.87 37.66 37.62 37. 91 38.34 36.88 37 .16 37.67 37.68 TI02 .05 .07 .05 AL20l 22.09 21.98 22.26 22.09 22.49 22.33 21.46 21.66 21.85 22.05 CR20l .07 FEO 12.83 12.57 21.95 28.38 21.74 27.53 30.58 29.85 29.04 29.94 HHO 1S.S9 15.51 2.28 2.24 2.25 2.11 3.49 3.25 3.01 l.05 ttGO 8.88 8.94 8.38 7.95 8.81 8.38 ~.38 6.00 1.06 6.23 CAO 2.14 2.12 1.57 1.65 1.63 1.72 1.60 1.61 1. 61 1.63 Hft20 .02 K20

TOTAL 100.38 100.06 1 oo. t's 100.00 100.83 100. 61 99.39 99.53 100.24 100.58

1111 ftTOftIC PROPORTIOHS BASED Ort SEL£CT£D HO.' Of OXYGEHS 1111

OX\'GEH 12 12 12 12 12 12 12 12 1Z 12

SI 2.980 2. 991 2.930 2.939 2.924 2.959 2. 951 2.953 2.953 2.955 TI .003 .004 .003 AL 2.001 1.994 2.041 2.034 2.045 2.032 2.024 2.029 2.019 2.038 CR .004 FE2+ .824 .809 1.819 1.854 1.790 1. 777 2.046 1. 984 1. 904 1. 964

"" 1.015 1. 011 .150 .148 .147 .151 .237 .219 .200 .203 ttG 1.017 1.025 .972 .925 1.013 .964 .642 . 711 .825 .728 CA .176 .175 .131 .138 .135 .142 .137 .137 .135 .137 HA .003 K

sun 8.019 8.008 8.046 8.042 8.033 8.025 8.037 8.032 8.0:l7 8.025

'll1t1r1t SAftPLE DIRECTORY 1l'fi1WI

SftttPLE HO. DESCRIPTIOH SftftPL£ HO. DESCRIPTIOH ---------- ----------- ---------- -----------

81 JE-20 86 JE-29 Rin 82 JE-20 87 JE-31 CORE 83 JE-29 88 JE-31 Ritt 84 JE-29 89 JE-31 8S JE-29 CORE 90 JE-31

GARitET

SI02 37 .78 37 .14 37.48 37.54 36.66 37.04 38.46 38.53 38.10 37.28 TI02 HD HD .12 .05 Al20J 22.13 22.32 22.17 22.20 21.76 21.84 21.92 22.02 21.67 21.62 CR203 HD .05 .04 FEO 29.60 30.84 30.54 30.80 30.88 30.60 14.50 14.48 14.43 18. 74 nHO 4.34 5.2l ~.07 5.34 5.00 5.13 14.15 14.50 15.66 17.50 ft GO 6.60 5.31 5.78 5.10 5.21 5.17 8.15 8.19 1.02 3.36 CAO .70 .71 .61 .59 .62 .67 2.57 2.64 2.86 2.29 HA20 K20

TOTAL 101.15 101.55 101.65 101.57 100.13 100.45 99.80 100.38 99. 91 100.88

** ftTOftIC PROPORTIONS BASED OH SELECTED NO. OF OXVGEHS **

OXYGEH 12 12 12 12 12 12 12 12 12 12

SI 2.950 2.920 2.935 2.947 2.927 2.943 2.982 2.974 2.976 2.965 TI .007 .003 Al 2.036 2.068 2.046 2.054 2.048 2.045 2.003 2.004 1. 995 2.027 CR .003 .003 FE2+ 1. 933 2.028 2.000 2.022 2.062 2.033 .940 .935 .943 1.247 HH .287 .348 .336 .355 .338 .345 .929 .948 1.036 1.179 ftG .768 .622 .674 .597 .620 .612 .942 .942 .817 .396 CA .059 .060 .051 .050 .053 .057 .214 .218 .239 .195 HA K

sun 8.032 8.046 8.042 8.026 8.049 8.035 8.0111 8.023 8.017 8.017

~ SftftPLE DIRECTORY ~

SftftPLE HO. DESCRIPTION SAftPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

91 JE-32 CORI 96 JE-32 Rin 92 JE-32 Rift 97 JE-35 93 JE-32 CORE 98 JE-l5 94 JE-32 Rift 99 JE-35 95 JE-32 CORE 100 JE-16

GftRHET

5102 J7.55 J7.79 J7A5 J7.50 J7 .15 J7 .01 38.05 J7.94 37.76 38,oq

TI02 .05 .08 .11 .06 .09 .06 RL20J 20.73 20.87 20.61 21.00 20.55 20.63 21.70 21.61 21 .57 21.62

CR20l HD HD , HD HD .04

FEO 18.38 18.01 11.71 18.07 11.79 17.94 15. 70 16.57 16.79 16. 98

ft HO 17.39 17 .18 17 .42 17.33 17 .12 17.06 14.04 11. 70 11.70 11.53

ft GO :i.19 3.59 l.69 l.74 t64 3.56 8.56 9.07 9.20 9.22

CAO 2.36 2.31 2.42 2.36 ' 2.31 2.33 1.58 1.86 1.78 1.80

Hl\20 .02 K20

TOTftl 99.68 99.83 99.416 100.09 98.70 98.63 99.63 98.75 98.80 99.19

111t ftTOftlC PROPORTIOHS BASED OH SELECTED HO. OF OHYGEHS *N

OXYGEH 12 1·2 12 12 12 12 12 12 12 12

SI J.019 3.022 3.011 2.997 3.010 3.003 2.966 2.969 2.957 2.965

TI .003 .005 .007 .004 .005 .004 ftl 1.965 1. 967 1.955 1.978 1.963 1.97l 1.994 1.993 1. 991 1. 986

CR .003 FE2+ 1.236 1.205 1. 191 1.208 1.206 1.217 1.024 1.084 1.100 1.107

"" 1.184 1.164 1.187 1.173 1.175 1.173 .927 . 775 .776 .761

ftG .382 .428 .442 .445 .440 .431 .994 1.058 1.074 1.071

Cft .203 .198 .209 .202 .201 .203 .132 .156 .149 .150

HA .003 K r

sun 7.995 7.989 8.00J 8.009 8.004 8.005 8.037 8.0J5 8.047 8.041

friW<1r SftftPLE DIRECTORY 1ridl1t

SftftPLt HO. DESCRIPTIOH SftftPLE HO. DESCRIPTION

---------- ----------- ---------- -----------101 JE-36 106 JE-36 102 JE-36 107 JE-74 103 JE-36 108 JE-~2 CORE 104 JE-36 109 JI-82 Rift 105 J[-36 110 JE-ij2 CORI

GARllIT

SIOZ 37.96 37.57 37 .81 TI02 .05 .06 .05 Rl20l 21.58 21.97 22.09 CR20J f EO 16.55 18.74 18.00 ft HO 11.51 10.0l 9.01 nGo 9.19 8.49 9.61 CAO 1.85 2.03 2.16 HA20 K20

TOTAL 98.69 98.79 98.73

** ftTOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEHS **

OXYGEN 12 12 12

SI 2.969 2.949 2.945 TI .003 .004 .003 AL 1.990 Z.023 Z.028 CR fE2+ 1.083 1.230• 1.172 nH .763 .667 .594 nc 1.071 .993 1.115 CA .155 .171 .180 HA K

sun 8.0ll 8.036 8.038

*"'*" SftnPLE DIRECTORY 1n\'1n\'

SAnPLE HO. DESCRIPTIOH SftftPLE HO. DESCRIPTIOH ---------- ----------- ---------- -----------

111 J£-82 RIH 112 OF-7 113 Of-7

TOURHRLIK(

SI02 34.55 34.20 35.11 35.19 . 35.22 35.66 35.14 35.03 34.69 34.35 TI02 .82 .86 .63 .41 .75 .46 .73 .74 .75 .73 Rl20l 3:i.35 34.69 34.03 34.20 3:i. 78 33.59 34.34 34.93 35.10 35.11 CR203 HD .06 .06 .04 .05 .05 HD H20l HO 10.30 9.05 8.25 7.84 10.24 10.02 6.36 5.89 6.28 6.23 HHO .19 .27 .22 .18 .24 .21 .05 HD .09 HD HGO 4.16 4.54 5.44 5.89 4.34 4.67 6.57 6.75 6.42 6.82 CAO .51 1.04 .80 .79 .49 .51 .72 .79 .50 1.03 HR20 1.47 1.29 1.77 1. 71 1.77 1.67 1.82 1.68 2.03 1.72 K20 .14 .19 .07 .06 .11 HD .05 .13 .04 .07

TOTAL 85.51 86.13 86.J8 86.33 86.94 86.86 85.83 86.01 85.92 86.08

"* ATOHIC PROPORTIOHS BASED OK SELECTED tlO. OF OXYGEHS 1r1r

OXYGEK 31 31 31 31 .. 31 31 31 31 31 31

SI 7.318 7 .160 7.294 7.294 7.JJ6 7.412 7.268 7.213 7 .169 7.095 TI .1 J1 .135 .098 .064 .117 .072 .114 .115 .117 .113 Al 8.326 8.560 8.333 8.355 8.293 8.229 8.372 8.478 8.549 8.548 CR .010 .010 .007 .008 .008

.FE3+ FEZ+ 1.825 1.585 1.43J 1.359 1.784 1. 742 1.100 1.014 1.085 1.076

"" .034 .048 .OJ9 .OJ2 .042 .037 .009 .016 HG 1.J1J 1.416 1.684 1.819 1.J47 1.447 2.025 2.071 1.977 2.099 CA .116 .233 .178 .175 .109 .114 .160 .174 .111 .228 Hf\ .604 .524 .713 .687 .715 .. 673 .730 .671 .813 .689 K .OJ8 .051 .019 .016 .029 .013 .OJ4 .011 .018

sun 19. 707 19. 712 19.802 19. 811 19. 77J 19. 739 19.799 19. 782 19. 851 19. 871

'lrlrlrfl SAHPLE DIRECTORY 1l1Wnt

SRHPLE KO. DESCRIPTIOH SAnPLE HO. DESCRIPTIOH ---------- -----------

____ .. _____ -----------

1 BH L0-1 6 BH L0-1 2 BH L0-1 7 ABH.:.7 · 3 BH L0-1 8 ABH-7 4 BH L0-1 CORE 9 ABH-7 CORE 5 DH L0-1 RIH 10 ABH-7 Rin

TOURnALitn'.

5102 34.69 34.51 34.70 34.45 34.50 34.61 34.74 34.17 34.76 34.35 TI02 .78 .74 .79 .77 .74 .73 .67 .81 .78 .77 AL20l 35.05 34.95 34.74 35.12 35.44 35.33 J!i.17 35.15 35.31 35.15 CR20l .06 HD HD HD .06 .04 HD TE20l HO 5.98 6.19 6.01 6.15 5.94 6.ll 6.18 6.20 6.03 6.36 ft HO .04 HD HD HD HD .05 HD HD ft GO 6.75 6.79 6.76 6.88 6.73 6.98 6.87 6.85 6.87 6.89 CAO .97 1.06 .83 1.12 .78 1.20 .80 1.13 .90 1.21 HA20 1.69 1.72 1.80 1.73 1.77 1. 71 1.84 1.69 1.77 1.71 K20 .10 .09 .12 .10 .06 .07 HD .07 .10 .07

TOTAL 86.11 86.07 85.80 86.34 85.99 86.96 86.34 86.18 86.59 86.55 '

tr1r ATOnIC PROPORTIOHS BASED OK SELECTED HO. OF OXYGEHS *"

OXYGEK 31 31 31 31 31 31 31 31 31 31

SI 7 .149 7 .127 7 .177 7.096 7 .111 7.083 7 .143 7.057 7 .126 7.069 TI .121 .115 .123 .119 .115 .112 .104 .126 .120 .119 AL 8.514 8.508 8.470 8.526 8.610 8.523 8.523 8.556 8.532 8.527 CR .010 .010 .006 f[J+ F£2+ 1.031 1.069 1.040 1.059 1.024 1.083 1.063 1.071 1.034 1.095 nH .007

·' .009

HG 2.073 2.090 2.084 2.112 2.067 2.129 2.105 2.108 2.099 2.113 CA .214 .235 .184 .247 .172 .263 .176 .250 .198 .267 HA .675 .689 .722 .691 .707 .679 .734 .677 .704 .682 K .026 .024 .032 .026 ;016 .018 .018 .026 .018

sun 19.819 19.860. 19.839 19.880 19.828 19. 891 19 .861 19.882 19.850 19.897

trkitff SAftPLE DIRECTORY frln\'iill

·SllnPLE HO. DESCRIPTIOH SftnPLE HO. DESCRIPTIOH ---------- ----------- ---------- -----------

11 ABH-7 CORE 16 ftBH-7 Rin 12 flBH-7 RIH 17 flBH-7 CORI 13 ftBH-7 CORE 18 ftBH-7 RIH 14 ABH-7 RIH 19 flBH-7 CORE 15 ABH-7 20 flBH-7 Rin

EPIDOTE

5102 37.35 37.54 37.30 39.56 36.78 37.22 32.33 37.27 36.17 TI02 .07 t\L203 25.37 24.76 24.51 26.09 22.82 23.85 19.02 24.88 21. 79 CR20l F£203 12.20 12.57 12.97 11.20 11.17 11.14 3.64 10.81 8.06 FEO nHO 1.39 .62 .31 .76 3.35 2.12 11.18 .93 7.96 nGO HD .33 .07 .1l .05 CAO 22.29 23.52 23.14 22.20 22.52 22.61 19.56 23.37 21. 71 ltt\20 K20

TOTAL 98.69 99.01 98.23 99.81 96.97 97 .01 85.7J 97.39 95.74 '

** ATOnIC PROPORTIOKS BASED OK SELECTED HO. OF OXYGEKS **

OXYGEH 12 12 12 12 12 12 12 12 12

SI 2.827 2.837 2.840 2. 925 2.866 2.876 2.921 2.853 2.893 TI .004 t\l 2.264 2.206 2.199 2.27l 2.096 2.172 2.025 2.245 2.054 CR H3+ .695 . 715 .743 .623 .655 .6'18 .247 .623 .485 FE2+ ntt .089 .040 .020 .048 .221 .139 .856 .060 .539 nc .038 .008 .015 .006 Ct\ 1.808 1.905 1.888 1.759 1.881 1.872 1.893 1. 917 1.860 HA K

sun 7.689 7.702 7.689 7.627 7.7:18 7. 714 7.943 7. 713 7.838

***"' SAnPLE DIRECTORY *"'**

SAftPLE HO. DISCRIPTIOH SAnPLI HO. DESCRIPTIOH ----------

_____ .. __ ,. __ ---------- -----------

1 JE-16 6 JE-7 2 JE-16 7 JE-7 3 JE-16 s JE-7 4 J[-16 9 JE-7 5 JE-7

•

EPIDOTE

SI02 37.35 37.54 37.30 39.56 36.78 37.22 3Z.33 37.27 36.17 Tl02 .07 AL20l 25.37 24.76 24.51 26.09 22.82 23.85 19.02 24.88 21.79 CR203 FE20l 12.20 12.57 12. 97 11.20 11.17 11.14 3.64 10.81 8.06 rro nno 1.39 .62 .31 .76 tJ5 2.12 11.18 .93 1.96 nGO HD .33 .07 .13 .05 CAO 22.29 23.52 23. 14 . 22.20 22.52 22.61 19.56 23.37 21. 71 HA20 K20

TOTAL 98.69 99.01 98.23 99.81 96.97 97.01 85.73 97.39 95.74

"'* ftTOnIC PROPORTIOHS BASED OH SELECTED HO. Of OHYGEHS "*

OKYGEH 12 12 12 12 12 12 12 12 12

SI 2.827 2.837 2.840 2.925 2.866 2.876 2.921 2.8s3 2.893 TI .004 AL 2.264 2.206 2 .. 199 2.273 2.096 2.172 2.025 2.245 2.054 CR HJ+ .695 .715 .}43 .623 .655 .648 .247 .623 .'185 FE2+

"" .089 .040 .020 .048 . 221 .139 .856 .060 .539 HG .038 .008 .015 .006 Cft 1.808 1.905 1.888 1.759 1.881 1.872 1.893 1.917 1.860 HA K

sun 7.689 7.702 7.689 7.627 7.758 7. 714 7.943 7.713 7.838

CA .01 CR .01 CR .01 CR .01 CR .01 CA .01 CR .01 CR .01 CA .01 HS 50.00 ns 50.oo HG 50.00 ns 50.00 HG .00 nG .00 HS 50.00 HG .00 HG .00 FE 50.00 f[ 50.00 FE 50.00 fI 50.00 FE 99.99 f[ 99.99 FE 50.00 fE 99. 99 FE 99. 99

n: 50.00 n: so.oo n: 50.00 n: so.oo n: .oo n: .00 n: so.oo n: .00 n: .00

"'*"'* SRHPLE DIRECTORY *""""* SAHPLE HO. DESCRIPTIOH SAHPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

1 JE-16 6 JE-7 2 J[-16 7 J[-7 l JE-16 s J[-7 4 J[-16 9 JE-7 5 JE-7

AnPHIBOLE

SIOZ 53.25 53.35 53.60 53.56 53.29 50.98 45.08 44.0Z 4J.7l 4l.54 TI02 .26 .04 .14 .11 .10 .29 AL20J .12 .17 .18 .24 4.14 13.09 13.03 15.42 16.08 CR203 HD HD FEO 14.07 13.88 13.35 14.45 14.09 24.41 25.43 25.89 23.80 23.73 nHO 16.04 15.66 16.~7 16.04 14.5l .30 .27 .28 .58 .53 HGO 14.06 14.43 14.43 13. 90 15.19 18.03 13.84 1J.J2 13.34 13.33 CAO .13 .26 .18 .19 .27 .07 .12 .12 .51 .52 HA20 .06 . 14 .oa .12 .13 .26 . 1.09 .98 1.71 1.74 K20 HD

TOTAL 97.75 97.98 98.08 98.44 97.74 98.23 99.06 97.77 99.26 98.78

*" ftTOnIC PROPORTIONS BASED OH SELECTED HO. Of OXYGENS **

OXYGEN 24 24 24 24 . 24 24 24 24 24 24

SI 8.340 8.321 8.341 8.339 8.297 7.783 6.899 6.856 6.664 6.529 TI .030 .005 .016 .013 .021 .033 AL .022 .031 .033 .044 .745 2.361 2.392 2.770 2.909 CR FE2+ 1.843 1.810 1. 737 1.882 1.835 3.117 3.255 3.373 3.034 3.046

"" 2.128 2.069 2.145 2.115 1. 916 .039 .035 .037 .075 .069 nG l.282 l.354 l.347 l.225 l.525 4.102 l.157 J.092 3.030 3.049 CA .022 .043 .030 .032 .045 . 011 .020 .020 .083 .086 HA .018 .042 .024 .OJ6 .039 .077 .323 .296 .SO? .518 K

sun 15.657 15.670 15.655 15.662 15. 701 15.879 16. 066 16. 081 16.183 16.l43

frff'lrlt SAHPLE DIRECTORY 1rf<1rll

SAftPLE HO.· DESCRIPTION SAHPLE HO. DESCRIPTIOH ---------- ----------- ---------- -----------

1 BH-J 6 240 AG 56 2 BH-3· 7 240 AG 56 J BH-3 8 240 AG 56 4 Bff-3 9 ABN-6 5 BH-3 10 ABH-6

ftftPHIBOLE

SIOZ 43.39 41.05 41. 92·. 42.39 TI02 . 30 1.64 1.39 . .53 Al203 15.59 15. 91 15.81 19.02 CR20l .09 HO 24.04 9.50 9.59' 14.59 ft HO .49 .73 .70 .17 ft GO 12.98 14.56 15.03 18.49 CAO .. 56 11.22 11.22 .62 Ht\20 1.80 2 .17 2.15 2.08 K20 .67 .60 HD ZHO .09

TOTAL 99.24 97.45 98.41 98.00

1r1I' t\Tonrc PROPORTIONS BASED OH SELECTED HO. Of OXYGENS **

OXYGIH 24 24 24 24

SI 6.630 6.255 6.312 6.284 TI .034 .188 .157 .059 Al 2.808 2.857 2.806 3.323 CR .011 H2+ 3.072 1.211 1.208 1.809

"" .063 .094 .089 .021 nG 2.956 3.306 3.373 4.085 CA .092 1.832 1.810 .098 HR .533 .641 .628 .598 K .130 .115 ZH .010

sun 16.198 16.514 16.499 16.291

... 1rit'ft'ft SAftPLE DIRECTORY jljfr1Wlr

SRftPLE HO. DESCRIPTION SAftPLI HO. DESCRIPTIO!f ---------- ----------- ---------- -----------

11 t\BH-16 12 JE-A 13 J[-A 14 JE-G

- !

PYROXEHE

5102 q6.89 q6.16 q1 .17 52.47 52.81 51.79 50.58 50.ZO TI02 .1q .10 .11 .08 .10 Al20l 5.87 S.22 5.6B 1.53 8.44 CR203 HD no 8.30 8.75 10.29 15.26 1S.07 15.11 11.61 18.08 nHO 43.07 43.23 38.85 1.54 1.69 1.61 .16 .15 nGo 1.19 .46 t1l 26.37 26.86 25.92 2S.13 24.61 CAO .15 .98 .29 .27 .24 .21 .08 .12 HA20 .03 K20

TOTAL 99.60 99.58 99.76 101. 92 101.99 100.q3 101.17 101. 73

_'ldt ftTOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEKS **

OXYGEH 6 6 6 6 6 6 6 6

SI 2.027 2.007 2.009 1.861 1.871 - 1.86:! 1.817 1.798 TI .004 .003 .003 .002 .003 AL .245 .218 .241 .319 .356 CR F£2+ .299 .318 .367 .453 .447 .455 .529 .541

"" 1.573 1.592 1.402 .oq6 .051 .M9 .005 .005 HG .076 .030 .199 1.394 1.418 1.391 1.346 1.313 CA .007 .oq6 .013 .010 .009 .008 .003 .005 Hft .002 K

sun 3.978 3.993 3.992 4.013 4.017 4.012 4.021 4.021

*"""'* SftnPLE DIRECTORY tt'ldtit

SAnPLE MO. DISCRIPTIOH SAnPLE HO. DESCRIPTION ---------- ----------- ----------

_______ ,.. ___

1 BH-1 6 JE-ft 2 BH-1 7 JE-~

l BH-1 s JE-G 4 JE-ft 5 J[-A

•

OXIDES

SIOZ TI02 .17 .13 .15 .11 .13 .11 .07 HD HD .06 ALZOJ .51 .34 .35 -.33 .38 .28 .32 .08 .19 .13 CR203 HD FE20l 71.29 71.42 70.96 70.59 71.44 71.01 71.68 71.97 71.63 71.81 FIO 32.23 32.30 . 32.11 31.81 32.25 32.03 32.22 l0.67 30.51 30.71 ft HO .45 .30 .33 .34 .39 .24 .34 1.78 1.79 1.72 nso HD HD .04 HD .OS .04 CAO HA20 K20

TOTftl 104. 69 104.49 103. 90 103.ZO 104.59 103. 71 104.65 104.52 104.ZO 104.50

*" flTOllIC PROPORTIOHS BftSED OH SELECTED HO. OF OXYGIHS *"

OXYGEH 4 4 4 4 4 4 4 4 4 4

SI TI .005 .004 .004 .003 .004 .003 .002 .002 ftl .022 .015 .015 .014 .016 .012 .014 .003 .008 .006 CR FI3+ 1. 969 1. 978 1. 976 . 1. 979 1. 976 1. 982 1.982 1. 995 1. 990 1. 990 H2+ .989 .994 .994 . 991 . 991 .993 .990 .945 .942 .946 nH .014 .009 .010 .011 .012 .008 .011 .056 .056 .054 nG .002 .003 .002 CA HA K

sun J.000 3.000 3.000 3.000 3.000 l.000 J.000 .3.000 l.00.0 J.000

*""'* SftftPLE DIRECTORY 1rlt*11:

SftftPL£ HO. DESCRIPTIOH SftftPL£ HO. DESCRIPTIOH ---------- ----------- ---------- ----------

1 BH ME-2 6 BH ME-1 2 BH ME-2 7 BH ME-1 3 BH ME-2 8 BH-i 4 BH ME-1 9 BH-1 5 BH UE-1 10 BH-i

OXIDES

SIOZ TI02 .21 .25 .13 .16 .15 .14 ~.16 53.44 .09 50.91 AL203 .20 .83 .42 .34 .49 .2l CR20l HD

. ' HD .18 HD .13 .05 H203 69.58 68.58 69.42 69.15 69.64 70.11 60.31 .75 HO 29.48 31.38 31.41 31.36 31.61 32.04 44.63 44.75 26.95 44.84 ft HO 2.26 AS .31 .24 .30 2.19 2.18 .09 .86 nso HD KD HD HD till ltll .06 .05 CAO HA20 K20 ZHO .24

TOTAL 101. 75 - 101. 51 101. 72 101. 31 102.23 102. 71 100.02 100.37 87.86 97.47

*"' ftTOftIC PROPORTIONS BASED OK SELECTED HO. OF OXYGEHS 1r11

I OXYGEH 4 4 4 4 4 4 3 3 4 3

SI TI .006 .007 .004 .. 005 .004 .004 1.006 1.009 .003 .992 Al .009 .037 .019 . 015 .022 .010 CR .005 .005 .001

. FE3+ 1. 979 1. 949 1. 974 1.975 1. 969 1. 977 1. 990 .015 H2+ _ .932 . 991 .993 . 995 .. 994 1.004 .939 .938 .988 . . 971 nH .072 . 014 .010 .008 .010 ' .047 .046 .003 .019 nc .004 .002 CA HA K ZH .008

sun 3.000 l.000 3.000 3.000 3.000 3.000 1. 994 1. 992 3.000 2.000

*1r1rll SftftPLE DIRECTORY "'*** . SAftPLE lfO. DESCRIPTIOH SftftPLE HO. DESCRIPTIOH ---------- ----------- ---------- -----------

11 BH-3 16 240 AG 56 12 BHG-302 17 ABH-1 13 BllG-302 18 ABH-1 14 BHG-302 19 ABH-3 15 BliG-302 20 ftBH-5

OXIDES

SIOZ TI02 48.59 50.13 48.06 52.69 .05 .06 49.43 51.21 .15 AL20l 2A4 4.95 till .45 CR20l HD .07 .10 .06 .06 .04 .75 HD rr20J 4.98 4.16 8.66 .15 56.39 51.57 .79 69.71 69.86 . HO 42.02 4l.90 42.57 43.59 25.89 26.08 44.33 43. 91 31.n 31.73 ft HO .98 .67 .54 2.71 .05 HD .08 .12 HD nco .38 .04 HD .59 .19 .07 HD .16 CAO .03 .04 .60 .28 HA20 K20 -ZHO .44 .18 .27

TOTAL 96.98 99.45 100.00 99.7Z 85.85 83.36 94.68 95.ZB 102.18 10Z.40

'lr1I ftTOnIC PROPORTIOHS'BllSED OH SELECTED HO. or OXYGEHS 'lr1I

OXYGEH J 3 3 J 4 4 3 3 4 4

SI TI . 951 .959 .916 .999 .002 .002 . 99'2 ·1. 014 .004 AL .127 .261 .020 CR .001 .002 .002 .002 .001 .022 Hl+ .098 .080 .165 .003 1.868 1.733 .. 016 1. 978 1. 971 FE2+ .915 .934 .903 . 919 .95l . 974 .989 .%7 1.000 . 995 nK .022 .014 .012 .058 .002 .002 .003 nc .015 .002 .022 .012 .005 .009 Cft .001 .001 .028 .013 Hft K ZK .008 .006 .009

sun Z.000 2.000 2.000 2.000 3.000 J.000 Z.000 1. 985 3.000 3.000

- SllnPLE DIRECTORY -\ SftftPLE KO. DESCRIPTION SftftPLE HO. DESCRIPTION

---------- ----------- ---------- -----------21 ftBH-5 26 ftBH-16 22 ftBH-6 27 JI-19 23 ftBK-6 28 JE-i9 24 ftBH-13 29 Jr-29 25 ftBH-16 30 JE-it

OXIDES

SIOZ no2 .09 48.92 47.87 11.08 12.63 AL20l .ls .49 .14 CR20l .12 .04 HD .48 .17 TE20l 69.96 8.78 10.31 46.16 42.96 no 31 .80 36.25 15.11 38.91 42.06 ft HO .08 6.29 1.64 HD ft GO KD .72 .11 1.lO .09 CAO .07 ttA20 K20

TOTAL 10Z.4l 101.07 101.07 98.47 98.04

*A- ftTOttIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEHS *A-

OKYSEtt 4 l l 4 4

SI TI .003 . 917 .902 .118 .168 AL .015 .022 .006 CR .004 .001 .014 .005 f El+ 1. 976 .165 .194 1.327 1.252 H2+ .998 .756 .736 1.244 1.361 nlf .003 .133 .162 HG .027 .004 .074 .005 CA .002 HA

. K

sun 3.000 2.000 2.000 3.000 3.000

"*** SftftPLE DIRECTORY ****

SAMPLE HO. DESCRIPTION · SftftPLE HO. DESCRIPTION ---------- ----------- ---------- ------------

31 J[-A 32 J[-ft 33 J[-A 14 JE-G -35 JE-G

GAHHIH

SI02 TI02 ~D l\l203 57.00 57 .1l 57.65 57 .01 56.94 56.7q 56.60 56.96 56.74 56.92 CR203 .12 .10 .09 .12 .09 .09 .06 HO 12.30 11. 90 12.24 12.54 14.29 14.25 11.66 13.35 13.82 14. 01 HHO .Zl .19 .16 .22 .43 .44 .l6 .44 .44 .43 HGO 1. 98 2.04 2.09 2.05 1.60 1.69 1.69 1. 71 1. 81 1.83 CAO Hl\20 K20 ZHO 27.64 28.09 28.11 27 .61 26.50 26.60 28.72 26.83 26.77 26.75

TOTAL 99.29 99.45 100.34 99.55 99.85 99.81 99.09 99.29 99.58 99.94

1rt1 ftTOHIC PROPORTIOHS BASED OH SELECTED HO. OF OXVGEHS **

OXYGEN 4 4 4 4 ' q 4 4 4 q q

SI TI Al 1.993 1. 994 1.993 1. 988 1. 985 1.979 1. 991 1. 99l 1. 981 1. 980 ' CR .003 .002 .002 .003 .002 .002 .001 Hlt .003 .004 .005 .009 .013 .019 .008 .007 .019 .020 FE2t .302 .291 .296 .301 .l40 .333 .283 .325 .323 .326 HH .006 .005 .004 .006 .011 .011 .009 . 011 .011 . 011 HG .088 .090 .091 .090 .071 .075 .075 .076 .080 .080 CA HA K ZN .605 .614 .609 .603 .579 .581 .633 .588 .586 .583

sun 3.000 3.000 3.000 3.000 3.000 3.000 3.000 l.000 3.000 3.000

'lrtril'll SAHPLE DIRECTORY jt1rltfr

SAHPLE HO. D£SCRIPTIOH SAMPLE HO. DESCRIPTION

---------- ----------- ---------- -----------1 ADH-12 6 ADH-13 2 ABH-12 7 ABIH3 3 l\DH-12 8 ADH-13 4 AllH-12 9 ADH-13 5 l\BH-13 10 ADIHJ

I .• I. I

I,

\''

GAHHITE

SIOZ TI02 AL20l 51.44 56.92 58.98 59.47 59.38 58.95 59.47 59.91 55.93 56.54

CR20l . 11 .05 .05 .09 .16

HO 12.45 10.6Z 9.73 10.76 10.13 10.19 10.09 10.16 14.76 14.66

nNo .41 .z0 .33 .Z9 .31 .33 I .24 .29 .22 .29

HGO 1.86 1.66 1.66 1.70 1.65 1.68 1.62 1.61 1.24 1.18

CAO HA20 K20 ZKO 28.29 29.2Z 30.67 29.21 29.39 29.31 29.64 29.80 21.10 27.20

TOTAL 100.45 98. 70 101.37 101. 54 101.11 100.46 101.11 101. 78 99.34 100.03

** ATOnIC PROPORTIONS BASED OH SELECTED HO. OF OKYGEHS 1r1r

OXYGEli 4 4 4 4 ' 4 4 4 4 4 4

SI TI AL 1. 989. 2.0.06 2.019 2.023 2.027 2.026 2.030 2.031 1. 970 1. 977 CR .003 .001 .001 .002 .004 H3+ .011 .028 .019 rr2+ .295 .266 .236 .260 .250 .249 .244 .244 .341 .345 nrt .010 .007 .008 .007 .008 .008 .006 .007 .006 •

1007 nc .081 .074 .072 .073 .071 .073 .070 .069 .055 .052 Cft HA K ZH .614 .645 .657 .622 .629 .611 .614 .6ll .598 .596

sun 3.000 2.997 2. 991 2.987 2.986 2.987 Z.985 2.984 l.000 3.000

***" SAftPLE DIRECTORY #r111r1r

SftftPLE HO. DESCRIPTIOtl SAMPLE HO. DESCRIPTION

---------- ----------- ---------- -----------11 ftllll-1l 16 ABtH4 12 ADtl-14 17 ABIH4 il RBll-14 18 l!BH-14 14 ABH-14 19 ftDH-16 15 Allll-14 20 ABll-16

GAHKITE

SI02 TI02 ALZOl 56.26 57.05 56.02 · 57 .2e 56.01 56.9J 55.57 54.92 56.28 55.J1

CR203 .OS .07 .06 .05 .07 HO 15.10 15.26 15.09 14.81 14.85 14.94 16.45 12.46 13.26 16.45

nHO .22 .JO .29 .JO .25 .25 .36 .16 .JS .44

~GO 1.5l 1.36 1.51 1.49 1.45 1.53 2.50 2.15 1. 9l 2.08

CAO HA20 K20 ZHO 26.79 26.99 26.6l 26.94 26.53 26.82 23.93 ZS.32 27.60 24.86

TOTAL 99.98 101. 03 99.54 100.88 99.14 100.47 96.81 98.08 99.45 99.14

** ATOnIC PROPORTIONS BASED OH SELECTED HO. OF OKYGEHS t<ft

OKYGElt 4 4 4 4 4 4 4 4 4 4

SI ·. -TI AL 1. 965 1. 972 1. 965 1. 980 1.972 1. 976 1. 946 1. 952 1. 970 1. 941

CR .002 .002 .001 .001 .002

Ftl+ .033 .026 .035 .019 .027 .024 .054 .046 .030 .059

FE2t .341 .l48 .341 ~l44 .l44 .344 .355 .268 .300 .350

HH .006 .007 .007 .007 .006 .006 .009 .004 .010 .011

HG .068 .059 .067 .065 .065 .067 .111 .097 .085 .092

CA HA K ZK .586 .585 .585 .583 .585 .583 .525 .631 .605 .546

sun 3.000 3.000 3.000 3.000 J.000 3.000 3.000 3.000 3.000 3.000

1<1<1<1< SRHPLE DIRECTORY -SAHPLE HO. DESCRIPTIOH SAMPLE HO. DESCRIPTIOH

---------- ----------- ---------- -----------21 AllK-16 26 ABtH6 22 ABK-16 27 ABtl-J 23 ABtl-16 28 ADH-3 24 ABH-H.1 29 ABH-3 25 ABtH6 30 ABH-3

GAHHITE

SIOZ TI02 AL203 55.13 55.29 56.31 55.99 56.05 55.64 56.64 57.08 56.57 56.07 CR20l .05 .15 .34 .21 .42 .33 HD .04 FEO 16. 95 15.49 9.76 14.97 14.92 13.93 14.10 Zt.56 23.79 9.37 HHO AB A6 .28 .29 .39 .35 .30 .14 .15 .14 HGO 2.36 1. 87 .82 1.30 1.28 1.27 1.36 5.76 6.78 ' 1.35 CAO HAZO K20 ZHO 22.70 25.36 32.71 26.77 26.42 27.80 27.78 14.57 11.88 33.11

TOTAL 97.62 98.52 100.03 99.56 99.17 99.31 100. 51 99.13 99.17 100.09

""" ATOnIC PROPORTIONS BASED OH S£L£CT£D MO. Of OXYGENS **

OXVCEH" 4 4 4 4 4 4 4 4 4 4

SI TI Al 1. 952 1. 954 1. 986 1. 967 1. 975 1. 964 1. 971 1.926 1.895 1. 972 CR .001 .004 .008 .005 .010 .008 .001 fE3+ .048 .045 .011 .025 .020 .027 .021 .073 .105 .027 f£2+ .378 .343 .234 .346 .350 .320 .327 - .443 .460 .207 HH .012 .012 .007 .007 .010 .009 .008 .003 .004 .004 HG .106 .084 .037 .058 .057 .057 .060 .246 .287 .060 CA HA K ZH .504 .561 .723 .589 .583 .615 .606 .308 .249 .730

sun 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 . 3.000

1r1r'lt1r SAnPLE DIRECTORY ***"' SAHPLE HO. DESCRIPTION SAHPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

31 ABH-3 36 ABH-4 32 ABH-3 37 ABH-4 33 ABH-4 38 ABH-6 34 ADH-4 39 ADH-6 35 ABH-4 40 ADH-9

GAHHITE

SI02 TI02 llL20J 55.88 56.53 56.37 55.96 56.05 55.79 55.87 55.69 56.38 56.11 CR20l .07 .04 . 11 .07 HD .06 .14 .09 FEO 9.59 9.56 9.00 9.82 9.M 9.79 9.78 9.77 9.97 9.23 ttHO .15 .17 .22 .20 .21 .21 .19 .23 .26 .18

nco 1.37 1.38 1.36 1.36 1.38 1.36 1.39 1.29 1.35 1.39 CAO HA20 K20 ZHO· 32.87 32.86 32.99 33.03 32.69 32.59 32.95 32.82 32.39 32.78.

TOTllL 99.93 100.54 99.94 100.48 100.04 99.74 100.21 99.86 100.49 99.78

'lrlr ATOnIC PROPORTIONS BASED OH SELECTED NO. OF OXVGEHS **

OXYGEH 4 4 4 4 4 4 4 4 q 4

SI TI AL 1. 968 1. 977 1. 982 1.962 1. 971 1. 968 1. 963 1. 965 1. 973 1. 977 CR .002 .001 .003 .002 .001 .003 .002 FE3+ .030 .022 .0111 .035 .027 .032 .036 .Ol4 .024 .021 FE2+ .210 .215 .207 .209 .213 .214 .208 .211 .224 .210 ttH .004 .004 .006 .005 .005 .005 .005 .006 .007 .005 HG .061 .061 .060 .060 .061 . 061 .062 .058 .060 .062 CA Hll -· K ZH .725 .720 .727 .726 .720 .720 .725 .726 .710 .724

sun 3.000 3.000 3.000 J.000 3.000 3.000 3.000 3.000 3.000 3.000 J - SAnPLE DIRECTORY 11'/rlr"ll

SllnPLE HO. DESCRIPTIOH s11nPL£ HO. DESCRIPTION ---------- ----------- ---------- -----------

41 A~H-8 46 ADH-8 42 ABtt-8 47 ABH-8 43 ADH-8 48 ADH-8 44 ABH-8 49 ABH-8 45 RBH-8 50 RBH-8

GRHHITE

SI02 TI02 AL203 58.38 58.80 59.02 57 .76 58.27 57.79 55.66 55.61 56.19 55.72 CR203 .37 fEO 13.88 14.32 13.59 13.57 1:i.95 13.61 1:i.92 12.66 8.52 9.88 HHO .29 .31 .32 .32 .37 .28 .41 .39 .32 .32 HGO :LS4 l.95 :L58 3.32 l.41 3.61 2.05 2.19 1.77 1. 91 CAO HA20 -K20 ZHO 24.69 24.32 25.27 24.65 24.89 24.23 21.42 28.15 33.56 . 31.50

TOTAL 101.08 101. 70 101. 78 99.62 100.89 99.52 99.83 99.00 100.36 99.33

** ATOMIC PROPORTIONS BASED OH SELECTED HO. OF OXYGENS **

OXYGElf 4 4 4 4 '4 4 4 4 4 4

SI TI AL 1.973 1. 973 1. 984 1. 986 1. 979 1. 984 1. 945 1.956 1. 966 1.964 CR .009 -fE3+ .027 .027 .016 .014 . 021 . 016 .046 .044 .034 .036 H2t .306 . 314 .308 .317 .315 .315 .299 .272 ·.178 .211 HH .007 .007 .008 .008 .009 .007 .010 .010 .008 .008 HG .164 , 168 I .152 .144 .H6 .157 .091 .097 .078 .085 CA HR K ZH .523 . 511 .532 . 531 .530 .5Z1 .600 .620 .736 .696

sun l.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 .3.000 3.000

- snnPLE DIRECTORY fn'<fn'<

SAMPLE HO. DESCRIPTIOH ~llMPU HO. DESCRIPTIOH

---------- ----------- ---------- -----------51 RBH-9 56 ADH-9 52 ABH-9. . 57 AEH-10 53 RBli-9 58 ADH-10 54 ABH-9 59 ABH-10 55 AfiH-9 60 ADH-10

GAHHITE

SIOZ TI02 AL203 56.98 56.49 56.54 56.08 . 56.36 56.82 56.94 56.94 56.85 56.54

CR20J HO 13.17 15.23 15.27 15. 76 12. 61 14. 97 15.74 15.57 15.78 15.06

HHO .28 .27 .23 .26 .22 .31 .29 .28 .24 .27

HGO 1. 50 1.57 1.42 1.36 1.41 1.57 1.58 1.64 1.59 1.31

CAO HA20 K20 ZHO 27.59 25.76 26.31 25.65 28.44 25.38 25.31 25.38 25. 41 25.57

TOTAL 99.52 99.32 99.77 99.11 99.04 99.0:i 99.86 99.81 99.87 98.7:i

** ATOnIC PROPORTIOHS DASED OH SELECTED HO. OF OKVGEHS 1r11

OXYGEH 4 4 4 4 4 4 4 4 4 4

SI TI AL 1.994 1. 979 1. 976 1. 974 1.988 1.993 1.982 1.983 1.980 1. 993

CR fE3+ .006 .021 .024 .026 .012 .007 . 011! .017 .020 .007

FEZ+ .322 .358 .355 .367 .303 .365 .371 .367 .370 .370

nH .007 .007 .006 .007 .006 .008 .007 .007 .006 .007

HG .066 .070 .063 . 061 .063 .070 .070 .on .070 .058

CA HA K ZH .605 .566 .576 .566 .628 .558 .552 .554 .554 .565

sun 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 l.000

Mdr1< SAnPU: DIRECTORY 1n'nWI

SAftPLE HO. DESCRIPTIOH SAnPLE tlO. DESCRIPTIOH

---------- ----------· ---------- -----------61 A9H-11 66 ABH-11 CEHTRE 62 ABH-11 67 ABH-11 RIH 63 ABH-11 68 ABIH 1 CEHTRE 64 ABH-11 69 ABK-11 RIH 65 ABH-11 70 ABH-11

/

GAHitIH

SI02 TI02 AL20l 56.82 57.53 58.86 58.33 58.23 57.62 58.35 57.89 58A3 58.69 CR203 .07 .07 .15 .07 .06 FEO 15A9 15. 99 15.54 15.36 1~.52 16.35 15.63 15.73 15.56 15.09 HNO .30 .14 .13 .20 .14 .14 .15 .14 .16 .17 HGO 1.17 1.84 1. 98 2.09 1.98 1. 95 2.02 2.01 2.08 2.09 CAO NA20 K20 ZHO 25.83 23.85 24.79 24.34 24.00 24.08 24.42 24.56 24.18 24.73

TOTAL 99.61 99.35 101 . 37 100.3? 100.0Z 100.1 q 100.64 100.39 100 .41 100. 77

irlr ATOHIC PROPORTIONS BASED OH SELECTED HO. OF OXYGENS 1r11

OXYGEN 4 4 4 4 4 4 4 4 4 4

SI TI Ill 1.989 Z.001 2.003 2.003 2.005 1. 990 2. 001 1. 993 2.005 2.006 CR .002 .002 .003 .002 .001 f El+ .011 .010 .005 f£2+ .374 .395 .375 .374 .379 .390 .380 .379 .379 .366 HN .008 .003 .003 .005 .OOl .003 .004 .003 .004 .004 HG .052 .081 .085 . 091 .086 .085 .088 .088 ;090 .090 CA HA K ZH .567 .520 .529 .524 .518 .521 .525 .530 .520 .530

sun 3.0,00 3.000 2.997 2.998 2.996 3.000 2.999 3.000 2.998 2.997

tttt1dr SllHPLE DIRECTORY irfrtttt

SllHPLE HO. DESCRIPTION SllHPLE HO. DESCRIPTION ---------- ----------- ---------- -----------

71 ADN-11 76 SK-2 CIHTRE 72 SK-2 CENTRE 77 SK-2 RIH 7l SK-2 RIH 78 SK-2 CENTRE 74 SK-2 79 SK-2 RIH 75 SK-2 80 SK-2

GAHffITE

SIOZ TI02 AL20J 58.26 58.85 51.86 58.71 58.39 57.89 51.34 57.90 51.71 57.73 CR20l .08 .10 .23 .26 .26 .26 .24 .24 HO 14.91 15.57 16.74 15.82 24. 71 24.84 24.89 24.90 25.50 25.54 nHO .20 .18 .36 .31 . 4() .28 .37 .32 ft GO 2.05 1. 97 Z.04 2.04 l.64 3.41 l.40 3.56 l.48 3.41 CAO HA20 K20 ZHO 2S.03 24.23 2J.78 24.02 1trn 13.16 13.15 12.93 13.31 13.21

TOTAL 100.53 100. 72 100.60 100.59 100.51 99.87 99,44 99.83 100. 61 100.45

1n'I ATOnic PROPORTIONS BASED OH SELECTED HO. OF OXYGENS **

OXYGEH 4 4 4 4 4 4 4 4 4 4

SI -TI AL 2.001 2.010 1.987 2.009 1. 964 1. 963 1.955 1. 962 1. 946 1. 950 CR .002 .002 .005 .006 .006 .006 .005 .005 f [3+ .013 .031 .031 .039 .032 .049 .045 FEZ+ .363 .377 .395 .384 .559 .567 .563 .566 .561 .567

"" .005 .004 .009 .008 .010 .007 .009 .008 HG .089 .085 .089 .088 .155 .146 .147 .153 .148 .146 CA HA K ZH .539 .519 .512 .515 .278 .280 .281 .2·74 .281 .Z80

sun 2.999 2.994 3.000 Z.996 3.000 3.000 3.000 3.000 3.000 3.000

- SAMPLE DIRECTORY -SAHPU HO. DESCRIPTION SflnPLr HO. DESCRIPTION

---------- ----------- ---------- -----------81 SK-2 86 SK-3 82 SK-2 87 SK-3 83 SK-2 CEHTRE 88 SK-3 CENTRE 94 SK-2 Rin 89 SK-l Rin 85 SK-l · 90 SK-3 CHITRE

GAHHITE

SI02 ..,

TI02 AL203 59.04 57.69 57 .61 57.49 57.53 57.B4 57.74 57.26 57.26 57.40 CR203 .21 .25 .28 .26 .19 .20 .11 .14 .14 .12 HO 25.04 24.69 24.63 24.71 25.27 25.57 21.39 21.46 21.31 20.95 nHO .33 .36 .36 .36 .34 .35 .23 .26 .28 .30 nco 3.37 3.30 3.50 3.62 3.64 3.50 2.78 2.78 2.60 2.89 CAO Hft20 K20 ZKO 13.17 14.03 13.33 12. 90 13.20 13.28 18.03 17. 90 18.28 18.39

TOTAL 100.16 100.32 99.71 99.34 100.17 100. 74 100.28 99.80 99.87 100.05

** ftTOnic PROPORTIONS BASED OH SELECTED NO. or OKYGEHS fr1t

OKYGEH 4 4 4 4 4 4 4 4 4 4

SI TI AL 1. 963 1. 953 1. 957 1. 957 1. 946 1. 947 1. 969 1.963 1.965 1.963 CR .005 .006 .006 .006 .004 .005 .003 .003 .003 .003 Fil+ .032 .041 .037 .037 .050 .048 .028 .034 .032 .035 FE2+ .569 .552 .557 .560 .556 .562 .489 .489 .487 .474 nH .008 .009 .009 .009 .008 .008 .006 .006 .007 .007 nG .144 .141 .150 .156 .156 .149 .120 .121 .113 .125 CA Kft K ZH .279 .298 .284 .275 .280 .280 .385 .385 .393 .394

sun 3.000 3.000 3.000 l.000 3.000 3.000 l.000 l.000 3.000 l.000 .

Afrtrft SAnPLE DIRECTORY 1rk1rfr

SAttPLE HO. DESCRIPTION SAnPL£ HO. DESCRIPTIOH ---------- ----------- ---------- -----------·

91 SK-3 Rift 96 SK-l 92 SK-3 CENTRE 97 SK-4 93 SK-3 Rin 98 SK-4 CENTRE 94 SK-3 CENTRE 99 SK-4 Rin 95 SK-3 RIH 100 SK-4 CEHTRf

\

GRHHIH

SI02 TI02 AL20l 51.89 57.70 58.75 57.52 58.18 57.70 56.66 56.30 56.33 55.69 CR20l .10 .05 .07 .11 .14 .13 .08 HO . 20.20 21.39 19.42 20.87 20.28 21.40 20.80 15.64 16.32 16.53

HHO . 21 .. 25 .22 .31 .27 .27 . l1 .17 . 21 .22

HGO 2. 91 2.83 2. 91 2.94 2.90 2.80 2.66 1.67 1.79 1. 78

CAO HR20 K20 ZHO 18. 93 17.90 19.08 18.41 18.59 18.38 18.49 25.70 24.34 24.29

TOTAL 100.24 100 .12 100.45 100 .16 100.36 100 .68 99.00 99.48 98.99 98.51

*" ATOHIC PROPORTIONS BASED OH SELECTED NO. OF OXYGEHS **

OXYGEN q 4 4 4 4 q 4 4 4 4

SI TI AL 1. 974 1.970 1.995 1. 964 1.980 1. 962 1. 962 1. 970 1. 975 1. 964 CR .002 .001 .002 .003 .003 .003 .002 FE3t .024 .029 .004 .034 .017 .035 .Ol6 .030· .025 .036 FE2+ .465 .489 .464 .472 .472 .481 .475 .358 .l81 .378 HH .005 .006 .005 .008 .007 .007 .008 .004 .005 .006 HG .125 .122 .125 .127 .125 .120 .116 .074 .079 .079 CR HR K ZH AM .383 .406 .394 .396 .392 .401 .563 .535 .537

sun 3.000 l.000 3.000 3.000 3.000 . · 3.000 l.000 3.000 3.000 3.000

1"'1rf< SftnPLE DIRECTORY 'lt1\'>\1'

SRHPLE HO. DESCRIPTION SRnPLE HO. DESCRIPTION

---------- ----------- ---------- -----------101 SK-4 RIH 106 SK-4 CENTRE 102 SK-4 CENTRE 107 SK-4 RIH 103 SK-4 RIH 108 SK-10 CIHTRE 104 SK-4 CIHTRI 109 SK-iO RIH 105 SK-4 RIH 110 SK-10

GAHHITE

SI02 TI02 AL203 57.47 56. 91 56.34 57.03 56.86 56.72 57.22 57 .13 57.08 57.03

CR20l .07 .09 .06 .06 .05 .18 .04 .06 .06 .06

HO 7.79 7.41 6.40 7.04 6.76 7.37 7.38 7.50 7.08 7.36

Htf O .59 .55 .47 .50 .47 .59 .52 .40 .49 .49

HGO 1.29 1.09 1.00 1.19 1.07 1.26 1.26 1.23 1.11 1.11

CAO tfA20 K20 ZHO 32.88 33.79 34.03 33.34 33.80 33.32 33.17 33.12 33.76 33.46

TOTAL 100.09 99.84 98.38 99.16 99.01 99.114 99.59 99.52 99.58 99.51

1n11 ATOMIC PROPORTIONS BASED OH SELECTED HO. OF OXYGEKS *"

OXYGEH 4 4 4 4 4 4 4 4 4 4

SI TI AL 2.008 2.003 2 .011 2.012 2.013 2.001 . 2.010 2.009 2.010 2.009 CR .002 .002 . 001 .001 . 001 .004 .001 . 001 .001 .001 F£2+ ;193 .185 .164 .176 .170 .184 .184 .187 .177 .184

nt1 .015 .014 .012 . 013 .012 .015 .013 . .012 .012 .012 HG .057 .049 .045 .053 .048 .056 .056 .055 .049 .049 CA HA K ZH .720 .745 .761 .737 .750 .736 .730 .730 .745 .738

sun 2.995 2.998 2.9'Jll Z.993 2.993 Z.997 2.99'1 2.995 2.994 Z.995

lr1r1rlr SftMPU DIRECTORY 1rlrfrlr

SftnPLE HO. DESCRIPTIOlf SAMPLE KO. DESCRIPTIOH

---------- -----------_,.._..,. ______

-----------111 BH-2 CENTRE 116 BH-2 112 DH-2 Rin 117 BH-2 113 BH-2 118 BH-2 CENTRE 114 DH-2 119 BH-Z Rin 115 DH-2 120 BH-2

GAHHITE

SIOZ TI02 ALWl 57 .61 56.112 56.84 56.49 56.99 56.09 56.38 56.37 56.89 56.59

CR203 HD HO 6.10 8.95 ·9.42 9.80 9.06 9.06 9.29 8.82 9.48 9.15

HllO .46 .34 .41 .46 .35 .35 .42 .35 .33 .41

ft GO . 94 1.10 1.14 .97 1. 01 1.15 1.10 1.03 1.12 1.03

CAO HA20 K20 ZHO 34.93 32.81 32.88 31.80 32.82 .32.71 31.84 32.85 32.20 JZ.30

TOTAL 100. 07 100.02 100.69 99.52 100. 23 100.16 99.03 99.42 100.02 99.48

.,. .. ATOnIC PROPORTIONS BASED Qlf SrLICTED HO. or OXYGEtlS *"'

OXYGEK 4 4 4 4 4 4 4 4 4 4

SI TI AL 2.018 1. 997 1. 986 1. 996 1.999 1. 996 1.999 1.995 1. 997 1.999 CR H3t .003 .014 .004 .004 .005 .003 H2t .152 .220 .220 .241 .225 .221 .233 .217 .234 .229 HK .012 .009 .010 . 012 .009 ·.009 . 011 I .009 .008 .010 nG .042 .049 .050 .043 .045 .051 .049 .046 .050 .046 CA HA K ZK .767 .722 .720 .704 .721 . 719 .. 707 .728 .7011 .715

sun 2. 991 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000

tttc1rtt SAnPLE DIRECTORY 1r111ttr

SAnPLE HO. DESCRIPTIOH SAnPLE HO. DESCRIPTIOH ---------- ----------- ---------- ------.. ----

121 BH-2 126 DH ME-1 122 BH UE-1 127 DH llE-1 123 BH UE-1 128 BH UE-1 124 DH UE-1 129 · DH U£:-1 125 BH UE-1 130 BH llE-1

. '

TABLE 1 GAHMITE

SI02 TIOZ AL20l 56.98 56.73 57.54 57 .16 56.06 57.04 . 56. 93 57.45 56.75 57.02 CR20J FEO 10.36 9.09 8.94 10.46 11. 96 9.03 8.98 8.90 8.48 8.89 HHO .5l .60 .67 .63 .88 .46 .47 .50 .41 .54 HGO 1.05 1.11 .98 1.08 1.03 1.00 1.06 1.11 1.00 1.10 CAO HA20 K20 ZHO 31.17 31. 71 32.60 31.08 29.35 32.29 32.17 32.20 32.45 32.47

TOTAL 100.09 99.24 100. 7l 100.41 99.28 99.82 99.61 100.16 99.09 100. oz

** ATOftIC PROPORTIONS BASED OH SELECTED HO. Of OXYGENS ~~

OKYG£H 4 4 4 4 4 4 4 4 4 4

SI TI AL 1.998 2.004 2. 005- 1. 997 1. 982 2.005 2.005 2.008 2.008 2.001 CR HJ+ .003 .018 FEZ+ .255 .228 .221 .256 .282 .225 .224 .221 .213 .221 HH .013 .015 .017 .016 .022 .012 .012 .Oll .010 . 014 HG .047 .050 .043 .048 .046 .044 .047 .049 .045 .049 Cft HA K Ztl :685 .702 .712 .680 .650 . 711 .710 .705 .719 .714

sun 3.000 2.998 2.990 3.000 3.000 Z.997 2.998 Z.996 2.996 2.999

**** SAftPLE DIRECTORY fmjt;lr

SAHPLE HO. DESCRIPTION SAHPU HO .. DESCRIPTION

---------- ----------- ---------- -----------131 . DH UE-2 136 DH UE-2 132 DH UE-2 137 BH UE-2 133 BH UE-2 138 BH UE-2 134 BH UE-2 139 DH UE-2 135 BH UE-2 140 DH UE-2 .

TABLE 1 GAHHITE

SI02 TI02 AL203 56.70 55.99 56.77 56.50 •57.23 56.67 56.43 56.47 56.45 55.37

CR20J .10 FEO 23.73 28.35 26.84 29.76 26.82 28.79 17.20 18.93 20.30 14.73

HHO 1.63 2.56 2.14 3.04 2.55 2.57 .09

HGO 2.00 1. 96 2.05 2.22 2.44 2.10 2.66 2.66 2.70 2.62

CAO HA20 K20 ZHO 15.52 10.29 12.05 8.26 11.30 9.62 23.14 21.94 20.57 26.49

TOTAL 99.58 99.14 99.85 99.78 100.34 99.74 99.53 100.00 100.11 99.21

** ATOHIC PROPORTIOHS BASED.OH SELECTED HO. OF OXYGEHS **

OKYGEH 4 4 4 4 4 4 4 4 4 4

SI TI Al 1.956 1. 934 1.947 1. 931 1. 9145 1.940 1. 956 1. 947 1.942 1. 938

CR .002

f[3+ .044 .066 .053 .069 .055 .060 .042 .053 .058 .062

HZ+ .537 .629 .600 .653 .592 .639 .331 .410 .437 .303

HH .040 .064 .053 .075 .062 .063 .002

nG .097 .096 .089 .0% .105 .091 .117 .116 .117 .116

CR HA K ZH .335 .222 .259 .177 .241 .206 .502 .474 .443 .581

sun 3.000 '3.000 3.000 3.000 3.000 '3.000 3.000 3.000 3.000 3.000

"*** s11nPLE DIRECTORY ****

SAnPLE HO. DESCRIPTIOH SAHPLE HO. DESCRIPTION

---------- --------------------- ----------141 BHG 302 146 BHG 302

142 DHG 302 147 240 AG 56

143 BHG 302 148 240 AG 56

144 BHG 302 149 240 AG 56

145 BHG 302 150 240 AG 56

TABLE 1 GRHHITE

SIOZ TI02 AL20l 55.89 55.63 54.87 57 .21 56.79 56.37 55.38 55.33 55.47 54.81 CRZ03 .07 .06 .05 . 11 .04 .04 .04 HO 16.26 16.65 11.88 11 .48 11.26 11.55 2.03 2.19 2.21 1.98 HHO .oa .42 .37 .43 HD .05 .04 HGO 2.S6 2.74 l.03 .55 .57 .59 .08 .08 .10 .07 CflO tlA20

;.• -., K20 ,..

ZHO 25.13 24.69 2l.24 29.80 . 30.57 30.05 41.58 41.87 42.03 41.92

TOTAL 100.14 99.86 99.02 99.52 99.61 99.10 99.14 99.56 99.89 98.78

** ATOHIC PROPORTIONS BASED OH SELECTED HO. OF OXYGEHS ""*

OXYGEN 4 4 4 4 4 4 4 4 4 4

SI Tl AL 1. 932 1.930 1. 915 2.013 2.004 2.000 2.001 1. 993 1. 992 1. 991 '

CR .002 .001 .001 .003 .001 .001 .001 H3+ .068 .069 .085 .006 .007 .009 FI2+ .331 .341 .358 .287 .282 .291 .052 .050 .049 .043 HK .002 .011 .009 .011 .001 .001 HG .125 .120 .134 .0211 .025 .026 .004 .004 .005 .003 CA HA K ZH .544 .537 .508 .657 .676 .668 . 941 .945 .945 .954

sun 3.000 3.000 3.000 2. 993 2.998 2.999 2.999 3.000 3.000 3.000 '·

Mrtm SAHPLE DIRECTORY Mr1t1t

SAHPLE HO. DESCRIPTIOH SAHPLE HO. DESCRIPTIOH ·.

---------- ----------- ---------- -----------151 240 AG 56 156 DPB-1 152 . 240 AG 56 157 JE-2 BLUE 153 2il0 AG 56 158 JE-2 BLUE 154 DPD-1 159 JE-2 BLUE 155 DPB-1 160 JE 2 BLUE

TABLE 1 GftHHITE \

SI02 Tl02 -AL20l 5S.62 57 .81 58.42 58.34 58.72 . 55.13 54.96 58.21 58.22 55.00

CR203 .29 . 21 .20 .25 . 11 .15 .08

HO 1.97 6.56 1.48 6.99 1.00 2.24 2.29 8.90 8.29 1.79

nHO .07 .20 .22 .20 .13 .04 .OS .18 .21 .10

nco .09 4.93 4.97 4.97 4.79 .13 .09 5.61 5.67 .06

CAO HD HR20 K20 ZNO 42.54 29.28 29.26 29.66 29.68 42.35 42.99 27 .61 21.88 45.53

TOTAL 100.29 99.07 100. 56 100.36 100.57 99.92 100.38 100.62 100.42 102.56

""' ATOftIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEHS ""'

OKVGIH 4 4 4 4 4 4 4 4 4 4

SI TI AL 1. 990 1. 985 1. 977 1. 979 1.988 1. 981 1. 971 1. 960 1. 963 1. 941 CR .007 .005 .005 .006 .002 .003 .002 Hl+ .010 .009 .019 .017 .006 .019 .029

. .038 .034 .045 FE2+ .040 .151 .162 .152 .162. .038 .029 .175 .164 HH .002 .005 .005 .005 .003 .001 .001 .004 .005 .003 HG .004 .214 .213 .213 .205 .006 .004 .239 .242 .003 CA · .001 HA K ZH .954 .630 .620 .630 .630 . 954 .966 .582 .589 1.007

sun 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 l.000

"llklrll SAttPLE DIRECTORY *"*""

SRftPLE MO. DESCRIPTION SAMPLE HO. DESCRIPTION

---------- ----------- ---------- -----------161 JE-2 BLUE 166 JI-3 BLUE 162 Jf-2 GRHH 167 JE-3 BLUE 163 JE-2 GREEH 168 JE-3 GREEN 164 Jf-2 GRHH 169 JE-3 GREEtl 165 JE-2 GRHH 170 JE-15 BLUE

TABLE 1 GAHHITE

. SIOZ TI02 AL203 55.34 55.H 54.93 54.19 54.42 55.39 5~ .. 54 55.75 56.06 56.26 CR203 .Ob .09 .09 .05 .04 FEO 1. 91 1.b9 1. 97 Z.14 1.78 1.82 1.83 1.85 1.53 1.40

. nHo .30 .10 .1b .15 HD nco .06 .OB .06 .22 .13 .07 .06 .07 .Ob .11 CAO HAZO KZO ZHO 42.95 43.11 43.67 42.93 43.33 42.qz 43.37 42.46 42.08 40.84

TOTAL 100.62 100.12 100. 63 99.73 99.75 99.70 100. 95 100.18 99.73 98.68

1\11' ftTOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEHS 1r1r

OXYGEH 4 4 ,, 4 4 4 4 4 4 4 4

SI TI AL 1. 978 1. 981 1. 9b7 1. 957 1. 966 1. 994 1. 979 1.996 2.009 2.024 CR .001 .002 .002 .001 .001 FEl+ .021 .019 .033 .041 .032 .006 .021 .003 HZ+ .028 .024 .017 . 014 .013 .040 .OZ5 .'044 .039 .036 nH .008 .003 .004 .004 nG .003 .004 .003 .010 .006 .003 .003 .003 .003 .005 CA HA K Ztf .962 .970 .980 . 971 . 981 .957 .968 .952 .945 . 921

sun 3.000 3.000 3.000 l.000 3.000 3.000 3.000 3.000 2.995 Z.987

'lhW<l'I SAftPLE DIRECTORY ... ~

SAftPLI HO. DISCRIPTIOH SAMPLE HO. DESCRIPTIOH ---------- ----------- ---------- -----------

171 JE-15 BLUE 176 JE-15 BLUE 172 J£-15 BLUE 177 JE-i5 BLUE 173 JE-15 BLUE 178 JE-15 BLUE 174 J£-15 BLUE 179 .JE-i5 BLUE 175 JE-15 BLUE 180 JE-14 DLU[

TABLE 1 GAHHITE

SIOZ TI02 AL20l 56.68 56.02 5~.J6 55.6J 55.55 55.40 55.15 55.19 58.57 58.59 CR20l HD .07 .05

HO 1.14 1.17 2.81 2.16 2.10 2.26 2.65 2.28 8.66 8.82

HHO .06 MD .05 .04 .09 .04 .48 .42

HGO .06 .04 .10 .2l .06 .14 .06 .16 6.02 6.01

CAO HA20 K20 ZHO 41.JO 41.60 41.51 41.95 42.05 42.08 42.16 42.16 21.00 27.M

TOTAL 99.24 98.86 99.86 100. 01 99.92 99.88 100.02 99.8J 100.78 100.88

#cir ATonrc PROPORTIONS BASED OH SELECTED HO. OF OXYGENS #cir

OXYGEN 4 4 4 4 4 4 4 4 4 4

SI TI AL 2.027 2.019 1.988 1. 992 1. 994 1.989 1. 981 1. 984 1. 961 1.960 CR .002 .001 FE3+ .011 .008 .004 .011 .019 .016 .OJS .040 HZ+ .029 .030 .060 .047 .049 .047 .048 .042 .167 .169 HH .002 .001 .001 .002 .001 .012 .010 HG .003 .002 .005 . 010 .003 .006 .OOl .007 .255 .254 CA tM K ZH I .926 .939 .934 . 941 .946 .947 .949 .950 .566 .567

sun 2.986 2. 991 J.000 J.000 J.000 J.000 J.000 J.000 J.000 J.000

1r1rlrk SAMPLE DIRECTORY 'lrllllil

SftHPLE HO. DESCRIPTION SAnPLE HO. DESCRIPTION .,. _________ ----------- ---------- -----------

181 JE-111 DLUE 186 JE-i8 BLU£ 182 JE-14 BLUE 187 JE-18 DLUE HlJ JE-18 BLUE 188 JE-i8 BLUE 184 JE-18 BLUE 189 JE-18 GREEN 185 JE-18 BLUE 190 JE-iB GREEN

TABLE 1 GRHHITE

SI02 TI02 llL20l 57.70 59.12 59.41 58.60 ·58.70 58.98 57.79 58.68 58.70 56.20 CR20J HD .10 .06 . ll .05 .10 .09 .08 .06 FIO 8.77 8.58 7.20 8.16 7.75 8.69 7.81 7.90 6.99 1.04 ttHO .50 .38 .31 .48 .38 .57 .34 .29 .33 HD nco 6.97 7.37 6.92 7 .17 7. 01 6.97 6.90 6.90 6.86 .14 CAO H/120 .;· -K20 ZHO 24.51 24.65 25.08 25.13 25.38 25.51 25.83 26.38 27.00 41.32

TOTAL 98.48 100.ZO 98.98 99.87 99.Z7 100.SZ 98.78 100.ZJ .99. 94 98.72

1r1r ATOnic PROPORTIOHS BASED OH SELECTED NO. or OXYGENS **

OXYGEH 4 4 4 4 4 4 4 4 4 4

SI -/ TI AL 1. 957 1. 964 1. 997 1. 958 1. 973 1. 957 1.958 1.960 1. 967 Z.OZ3 CR .ooz .001 .003 .001 .OOZ .ooz .ooz .001 FE3+ .043 .034 .039 .OZ6 . 041 .040 .038 .03Z FEZ+ .168 .168 .170 .159 .159 .164 .148 .149 .135 .OZ7 HH .01Z .009 .007 .01Z .009 .014 .008 .007 .008 HG .Z99 .310 .Z94 .303 .298 .Z9Z .Z96 . Z91 .Z91 .006 CA ·-HA K ZH .5Z1 .513 .528 .5Z6 .534 .530 .548 .55Z .567 .93Z

sun 3.000 3.000 3.000 l.000 3.000 3.000 3.000 3.000 3.000 Z.988

1r1r1r1r SRnPLE DIRECTORY 1r1r1rllr

SAHPLE KO. DESCRIPTION SAHPLE HO. DESCRIPTION

---------- ----------- ---------- -----------191 JI-19 GRHH 196 JE-19 GREEH 19Z Jf-19 GRHH 197 JE-i9 GRHH 193 JE-19 CREEH 198 JE-19 CRHH 194 Jf-19 CREEH 199 JE-i9 GREEH 195 JE-19 CRHH zoo JE-Zl BLUE

TABLE 1 GAHHITE

SI02 TI02 AL20J 56.26 57.05 55.80 60.39 60.67 60.08 60.54 60.83 60.37 60.H

CR203 .04 .05 HD HD .04

FEO 1.40 .81 1.61 5.31 5.23 4.96 4.72 4.97 4.84 4.84

HHO .06 HD .04 .l9 .32 .27 .28 .30 .l2 .l2

HGO .25 .11 .06 7.80 1.79 7.89 1.58 7.56 1.62 7.50

CAO HD HA20 KZO ZHO 41.65 42.01 42.64 26.23 26.38 26.56 26.57 26.81 26.83 27.00

TOTAL 99.64 100. 01 100.15 100.16 100.44 99.79 99.72 100.47 99.98 99.84

11'11 ATOMIC PROPORTIONS BASED OH SELECTED HO. Of OXYGEHS tm

OXYGEK 4 4 0 4 4 4 4 4 4 4

SI Tl AL 2 .. 012 2.026 0.000 1. 996 1.999 1. 991 2.008 2.005 2.001 1.999

CR .001 .001 .001

FEl+ .003 .006

FE2+ .Ol6 .020 0.000 .122 .122 .111 .111 .116 .114 .114

"" .002 0.000 .009 .008 .006 .007 .007 .008 .008

HG .011 .005 0.000 .326 .325 .ll1 .l18 .315 .319 .l15

CA .001 HA K ZH .933 .915 0.000 .543 .545 .552 .552 .554 .557 .562

sun 2.994 2.987 0.000 3.000 3.000 l.000 2.996 2.997 2.999 3.000

1rltfr1r SAHPLE DIRECTORY 1r1rfr1t

SAHPLE HO. · DESCRIPTIOH SftftPLE HO. DESCRIPTIOH

---------- --------------------- -----------201 JE-23 BLUE 206 JE-23 GREEH

202 J£-2l BLUE 207 JE-23 GREEH

203 JE-23 BLUE 208 JE-23 GREEH

204 J(-23 GRHH 209 JE-Zl GREEN

205 JE-2l GREEK 210 JE-23 GREEH

TABLE 1 GAHNITE

SI02 TIOZ AL203 60.52 55.39 54.89 55.26 55.20 54.32 56.07 56.55 56.57 59.72 CR203 .04 .04 .09 -FEO 4.98 1.68 1.84 2.48 2.25 . 2.02 1.JS 1.74 1.77 7.88 nHO .J1 .04 .09 .27 .23 .OS .10 .10 .10 .l5 HGO 1.4l .08 .13 .11 .11 .1l .12 .11 .10 6.21 CAO ND .04 HA20 K20 ZHO 21.13 4l.l1 42.13 42.JO 42.36 42.16 42.72 42.95 4l.l8 26.74

TOTAL 100. 41 '100.50 99.08 100.46 100.24 98.73 100.40 101. 45 101. 92 100.90

** ftTOnic PROPORTIONS BASED OH SELECTED NO. OF OXYGENS .,,.,,

OXYGEN 4 4 4 4 4 4 4 4 4 4

SI TI ftl 2,001 1.982 1.988 1. 976 1. 978 1. 977 2.001 1.998 1. 992 1.987 CR .001 .001 .002 f El+ .018 .012 .02l .019 .023 .008 • 013 FE2t .117 .024 .036 .040- .038 .030 .034 .042 .036 .173 nH .007 .001 .002 .007 .006 .002 .OOJ .003 .003 .008 HG .311 .004 .006 .005 .005 ' .006 .005 .005 .004 .261 CA . 001 . 001 HA K ZH .562 .971 .956 .948 .951 .. 962 .955 . 951 .957 .557

sun 2.999 J.000 3.000 3.000 3.000 3.000 3.000 J.000 3.000 J.000

111r1rlf SAnPLE DIRECTORY **** SftnPLE NO. DESCRIPTIOlf snnPLE HO. DESCRIPTION ---------- ----------- ---------- -----------211 Jf-23 GRHH 216 JE-39 BLUE

212 JE-26 BLUE 217 JE-74 BLUE 213 J£-J5 BLUE 218 JE-74 BLUE 214 JE-35 BLUE 219 JE-74 BLUE 215 J[-35 BLUE 220 JE-74 GREEH

TABLE 1 GAHHITE

SI02 1102 AL203 56.03 59.18 s:L17 53.29 5l.77 59.22 58.16 58.27 58.48 60.61

CR203 ..;

FEO .60 7.35 3.97 3.54 3.39 7.11 10.79 8.68 10.56 11.29

HHO .35 .10 .09 .12 .'1.7 .50 .38 ' .50 1.09

HGO 5.61 .11 .16 .14 6.00 6.38 4.99 6.21 12.36

CAO HR20 K20 ZltO 41.93 27.89 41.49 40.73 41.16 26.99 2l.20 27.25 2j.75 14.50

TOTAL 98.56 100.38 98.84 97 .81 98.58 99.59 99 .11 99.57 99.50 99.85

tm RTOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGEltS '11'11

OXYGEH 4 4 4 4 4 4 4 4 4 4

SI TI AL Z.024 1. 990 1. 941 1. 960 1. 962 1. 997 1. 964 1. 985 1. 970 1. 932

CR ·f[lf. .010 .059 .040 .038 .003 .036 .015 .030 .068

FI2+ .015 .165 .044 .052 .050 .167 .223 .194 .222 .137

nH .008 .003 .002 .003 .007 .014 .009 .012 .025

nc .239 .005 .007 . .006 .256 .272 .. 215 .264 .498 ;..

CR HA K ZH .949 .588 .949 . 938 . 941 .570 .491 .581 .501 .290

sun 2.988 l.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000

frfr1rl< SRnPn DIRECTORY trlrtrl<

SRnPLE HO. DESCRIPTIOH SAHPLE HO. DESCRIPTION

---------- --------------------- -----------

221 J£-74 BLUE 226 JE-&2 GREEH

222 JE-74 GREEH 227 OF-7 GREElt

223 J£-82 BLUE 228 or-7 GREEH

224 JE-82 BLUE 229 OF-7 GREEN

225 J£-82 BLUE 230 JE-i6

TABLE 1 GAHHITE

SI02 TI02 AL20J 60.29 54.68 62.77 61.25 61.33 61.22 61.19 61.41 61.06 61.09 CR203 .67 .15 .05 .07 .07 .. 11 1.15 . 71 1.45 HO 1:i.87 27.37 20.25 22.28 21.77 21. 91 21.87 20.37 2l.54 19.87 nHO 1.35 .39 .75 .90 .SS .so .S2 .07 nGO 1:i.13 6.23 1~.39 14.36 14.62 14.67 14.54 13.6B 1:i.14 14.55 CAO Hft20 K20 ZHO 11.08 8.31 .65 .49 .52 .67 .08 2.34 1.25 2.01

TOTAL 99.7Z 97.65 99.96 99.33 99.19 99.34 98.61 99.02 99.70 98.97

*"' ftTOnIC PROPORTIOHS BASED OH SELECTED HO. or OKY&EHS **

OKYGEH 4 4 4 4 4 4 4 4 4 4

SI TI Al 1. 911 1.866 1.929 1. 910 1. 911 1.906 1. 916 1. 930 1..915 1. 913

· CR .015 .003 .001 .001 .001 .002 .024 .015 .030 FE3+ .089 .119 .068 .089 .087 .092 .082 .046 .070 .057 fE2+ .223 .544 .373 .404 .394 .392 .404 .409 .454 .305 nH . 031 . 010 .017 .020 .020 .018 .018 .002 nG .526 .269 .598 .566 .576 .577 .576 .544 .521 .576 CA HR K ZH .220 .170 .013 .010 .010 .013 .002 .046 .025 .039

sun 3.000 3.000 3.000 3.000 3.000 3;000 3.000 3.000 3.000 3.000

***"' SftnPLE DIRECTORY ***"'

SAnPLE HO. DESCRIPTION SftnPLE HO. DESCRIPTIOH

---------- ----------- ---------- -----------231 J£-16 236 JE-n 232 JE-29 237 JE-A 233 Jf-ft 238 JE-~ 234 JE-ft 239 JE-G 235 Jf-ft 240 JE-~

SIOZ TI02 l\L20J 61. 27 CRZOl .42 FEO 22.74 HHO ttGO 1l.65 CAO HAZO K20 ZHO 1.07

TOTAL 99.15

OXYGElt 4

SI TI Ill 1.922

. CR .009 FEl+ .069 FEZ+ .437 ftH ftG .542 Cl\ HA K ZH .021

sun l.000

SAnPLE HO.

TABLE 1 Gl\HHITE

tr11. ATOnIC PROPORTIOHS BASED OH SELECTED HO. OF OXYGENS tr11.

"""** SRnPLE DIRECTORY *1r1r11

DESCRIPTIOH SAnPLE HO. ·

241 JE-G

1 9 AUS 1988

DESCRIPTION